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most favourable oppositions occur when Mars is near its perihelion (II, Figs. 1 and 2), with the earth near its aphelion (a), point. The ideal condition would be for opposition to take place about the last week

in August, whilst the most unfavourable conditions would obtain if it occurred about the third week in February; thus the opposition of 1877 was the most favourable during last century, except that of 1845, whilst that of 1901, February 21, was about as unfavourable as is possible.

The advantage of proximity was well illustrated in 1877, when Asaph Hall discovered the two Laputan satellites, and Schiaparelli first observed the muchdiscussed canali.

On September 23, when at opposition, Mars will be about 364 million miles from the earth, but the nearest approach of the two bodies will take place on September 18, when the distance separating them (E,-M,, Fig. 2) will be about 160,000 miles less. After the opposition, as the planet lags behind the earth, as shown in Fig. 2, the distance will continue to increase, and the apparent diameter of the planet will, of course, decrease, as shown by the circles drawn on the right of the diagram. These circles show the relative apparent diameter of the planet on August 13, when

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at least distance from the earth, and on November 1, when

substantial a

increase in the distance

and astronomers the world over are once more seizing | Mars is at perihelion, on September 18, when the opportunities presented by a favourable opposition for the further solution of the Martian enigma. The actual opposition will not take place until September 23d. 22h., or 10 a.m. on September 24, civil date.

[graphic]

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As Prof. Lowell says in his classical memoir on Mars, Study of Mars at one opposition is material to its study at the next. . . . At any one opposition we may scan Mars but for a few months through only a fraction of its circuit round the sun." Therefore, no opportunities may be missed by the students of the ruddy planet, whenever, and under whatever conditions, an opposition takes place. But only at one opposition in every seven, or about once every fifteen years, are the conditions, so favourable as at present; Figs. 1 and 2 show this diagrammatically. The orbits of the earth and Mars are drawn to scale, but as eccentric circles, and irom Fig. 1 it will be seen that the opposition of this month will be, as regards the distance separating the two planets, the most favourable we have experienced since 1892. Owing to the eccen

tricity of the planet's orbit, the distance between the earth and Mars, when at an opposition, may range from 61,000,000 to 35,000,000 miles, the corresponding range of the apparent diameter being 13" to 25". The

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FIG. 2.

separating the two bodies will have taken place. The following are the apparent diameters of the planet at different epochs during the present opposition:September 1, 22'8"; September 18, 24"; September 23

moon.

(opposition), 23'9"; October 1, 23'3"; November 1, 1787; December 1, 12'7". This means that on September 18, an observer using a power of x 80 would see Mars on the same scale as a naked-eye observer sees the moon; the conditions of " seeing would be worse. Taking another illustration, a land area of about the size of Ireland would, roughly speaking, appear as a spot of 13" diameter, or a little longer than 1/1500th of the apparent diameter of the full Whilst the distance of the planet is an important factor in determining the value of the observing conditions at an opposition, it is by no means the sole factor; the altitude of the planet above the horizon makes or mars the conditions for the users of large instruments searching for minute detail. Thus, although the opposition of 1892 produced a more favourable distance-condition than that of 1894 (see Fig. 1), the observing conditions at the latter were not inferior, because of the higher culmination of the planet. At the present opposition, the declination of Mars is 4° S., and this means that for observers in our latitude (51° 30') the meridian altitude will not exceed 35°; but this is a great improvement on the conditions in 1907, when the corresponding altitude was only 100, and when, even from Flagstaff, Prof. Lowell found it desirable to send an expedition to the Andes for the observation of the planet. During the present opposition the meridian altitude at Flagstaff will be more than 50°.

As at all favourable oppositions, taking place about August, the south pole of Mars is now tilted earthwards, the earth, at the date of opposition, being about 20° below the plane of the planet's equator. Therefore the southern hemisphere will be observed, and as the summer solstice of this hemisphere, as shown in Fig. 2, occurs but a few days before opposition, the southern snowcap is in the process of dissolution, and changes due to the melting of the snow are taking place. Already such phenomena have been recorded by MM. Desloges and Jonckheere, among others. As the rotation-periods of the earth and Mars are approximately equal, the same regions can be observed on consecutive nights. On September 19 the Syrtis Major region will be in view, and on September 27 the region of the Mare Cimmerium.

Probably at no opposition since the time that Fontana suspected markings on the ruddy planet, in 1636, has the status of areographers been so critical as at the present juncture. Thanks to the persistent labours and unswerving faith of a few observers, of whom Prof. Lowell is the foremost, the question as to the subjective reality of the canali discovered by Schiaparelli in 1877 may be considered as settled. Whether one follows Prof. Lowell's lead in the matter of "artificial, irrigating waterways" or not, there can remain but little, if any, doubt that these long, straight channels do exist. In describing his observations, made at Trincomali, Ceylon, during the unfavourable opposition of 1903 (see Fig. 1), when the apparent diameter of the planet was but 14'6", the late Major Molesworth said' :-" Personally, I am quite convinced of the reality of the great majority of the so-called canals: I think I could convince the most sceptical on this point if they could only have spent an hour or two at my telescope on some of the perfect nights in March and April this year." Major Molesworth used a 12-inch Calver reflector, with a power of 450. Numerous observers, and the Flagstaff photographs, have also testified as to the gemination of these features. Not only do these canals exist, but, in the opinion of many experienced observers, 1 Monthly Notices, vol. Ixv., No. 8, p. 839, 1905.

they also suffer changes which show a dependence on the seasonal changes of the planet.

Having settled the existence of the "canals," it became necessary to account for the changes, and, in one essential, this question remained more or less open until the opposition of 1907. With regard to the polar caps, Herschel's observations enforced the natural conclusion that their changes were due to the accumulation and dissipation of "snow" as the Martian winters waxed and waned. This coincidence of snowcap and season was not to be denied, and in the Martian spring, at the opposition of 1892, Prof. W. H. Pickering observed the disappearance of some 1,600,000 square miles of the southern snowcap, an area about the size of India, in a period of thirty-three days. But there still remained the one essential factor, that was the proof that this snow was really frozen water; that the Martian atmosphere contained watervapour sufficient to produce these effects. On this point the different observers were at issue.

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Beer and Mädler, during 1830-9, found that occasionally certain permanent features of the planet's landscape were blurred, as though by passing cloud and mist. During the favourable opposition of 1862, Lockyer's observations led to the definite conclusion that the daily nay, hourly-changes in the detail and in the tones of the different parts of the planet were caused by the transit of clouds over the various features.

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1

"Clouds and mists " and "polar snows" inevitably suggest to the terrestrian the presence of water, hence a raison d'être for the canals, and the spectroscopic evidence adduced by Huggins and Vogel went to confirm the suggestion. But with the spectroscopic equipment of the Lick Observatory at their disposal, Campbell and Keeler could find no evidence for watervapour in the planet's atmosphere, and the critics of a terrestrial" Mars suggested that the snowcaps might be caused by the solidification and deposition of some other compound, such as carbon dioxide.

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However, the spectrograms obtained by Mr. Slipher at the last opposition, 1907, afford, according to our present view, incontrovertible evidence that the atmosphere of Mars does contain a detectable quantity of water-vapour (see NATURE, vol. lxxvii., p. 442, March 12, 1908). Prof. Very estimates that at the time the spectrograms were taken, the Martian atmosphere contained sufficient precipitable water to give an average layer 14 mm. deep, or about one-third or one-fourth that in the earth's atmosphere. Nor is water-vapour the only familiar atmospheric constituent which has been shown to be present by the Lowell Observatory spectra. When Mr. Slipher described the 1907 spectra, he explained the difficulty of detecting the free oxygen constituent of the Martian atmosphere, viz., the probable relatively slight increase in intensity, of the oxygen bands, produced by adding the absorption of a thin (Martian) atmosphere to that of a dense (terrestrial) atmosphere, but expressed the opinion that "its detection need not be considered impossible.'

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2

A recent message from the Kiel Centralstelle, dated September 10, informs us that Prof. Very's measures of the Lowell Observatory spectrograms-which show the spectra of the moon and Mars photographed side by side when the respective objects are at equal altitudes-show that oxygen is present in the atmosphere of Mars; the relative intensification of the oxygen band b, in the planet's spectrum, is stated to be eight times the probable error of the measures. Therefore, although the details are yet to come, it appears fairly

1 Memoirs R.A.S., vol. xxxii., p. 179, 1863.
2 Astrophysical Journal, vol. xxviii., p. 494, 1908.

safe to assume that not only water-vapour, but oxygen also, exists in the Martian atmosphere.

Thus we arrive at the present opposition with the knowledge that a familiar compound, capable of forming snowcaps, of filling canals, and of being pumped in order to irrigate the pastures of a thirsty landscape, exists on Mars, and is accompanied by that element which we terrestrians look upon as another essential for the existence of animal life; and crucial difficulties in the "habitability " theory have been removed. Close, persistent, and world-wide scrutiny, at this favourable epoch, should lead to further elucidation of the enigma, and enable us to "reconstruct " a being and a vegetation capable of

existing there.

An idea which has caught the popular fancy is that of signalling to Mars, but as the earth, from the planet, would be in the glare of the sun and would subtend, even at the impossible moment of opposition, an angle of less than 50"-of the same order as the apparent diameter of Jupiter at his recent opposition— to say nothing of the questionable transparency of our thicker atmosphere, this problem has not yet entered the province of practical astronomy. WILLIAM E. ROLSTON.

POLAR EXPEDITIONS AND OBSERVATIONS. THE HE position and prospects of polar exploration have been given great attention in the daily Press during the last few days. No precise information as to Dr. Cook's journey to the North Pole has yet been published, but the general narrative of Commander Peary's expedition leaves little room for doubt that Commander Peary reached the neighbourhood of the pole, and probably the pole itself, though an element of uncertainty must exist until his observations for latitude are examined critically. The Berlin correspondent of the Times reports that an executive committee for a Zeppelin polar expedition has been formed, the object of the expedition being defined as "the scientific investigation by means of the dirigible airship of the unknown Polar Arctic Sea and the development of the dirigible airship for the carrying out of scientific labours." Announcement has also just been made that a British Antarctic expedition will start next August under Captain R. F. Scott, who commanded the National Antarctic Expedition of 1900-4, with the object of reaching the South Pole.

As all the world knows, Mr. Shackleton's record of this year has given Great Britain the premier position in Antarctic exploration, and an earnest desire is felt by British explorers to place to the credit of this country the feat of first reaching the South Pole. McMurdo Sound has in the past been used as the base for British South Polar expeditions, but it is proposed on the next journey to establish a second base in King Edward VII. Land, 400 miles to the east of McMurdo Sound. The track to the pole from the new base may be expected to include phases similar to those met with in travelling from McMurdo Sound, but it is anticipated it will continue longer on the sea-level, meet the mountains nearer the pole, and consequently leave a shorter journey on the high inland plateau. The distance to be covered is in all some 1500 miles, for which 150 days are available. The plan for the journey to the pole from King Edward VII. Land includes the use of three means of sledge traction: ponies, a dog team with a relay of men, and motor sledges.

The scientific objects of Captain Scott's expedition are stated to be as follows:-(1) Geographical. To explore King Edward VII. Land, to throw further light on the nature and extent of the great Barrier ice

(4)

formation, and to continue the survey of the high mountainous region of Victoria Land. (2) Geological. To examine the entirely unknown region of King Edward VII. Land and continue the survey of the rocks of Victoria Land. (3) Meteorological. To obtain synchronous observations at two fixed stations, as well as the weather records of sledge journeys. Magnetic. To duplicate the records of the elements made by the Discovery expedition with magnetographs. The comparison should throw most important light on secular changes. (5) Miscellaneous.— In addition, attention will be paid to the study of marine biology at both stations and in the ship, and the examination of physical phenomena will be continued.

It is estimated that an expedition of the kind projected will cost at least 40,000l., and towards this sum considerable amounts have been given already. An appeal has been made to the public, and it is hoped that no difficulty will be experienced in raising the necessary money for the accomplishment of what will in any case include valuable scientific work.

The full narrative of Commander Peary's expedition to the North Pole appeared in the Times of September 11 and 13, and occupied six columns. By permission of the editor we are able to give a summary of this account of the journey and the observations made. The expedition left Etah, Greenland, on August 18, 1908, in the Roosevelt, having on board 22 Eskimo men, 17 women, 236 dogs, and about 40 walrus. Cape Sheridan was reached on September 5 and winter quarters were established there. Sledge loads of supplies were then taken to Cape Belknap, Porter Bay and other stages up to Cape Columbia, where Prof. McMillan obtained a month of tidal observations during November and December. Tidal and meteorological observations were also made at Cape Bryant, and explorations were carried on.

The expedition started for the north from Cape Columbia in several divisions at the end of February of this year. Latitude 83° 20' was passed on March 2, and on March 5 "the sun, red and shaped like a football by refraction, just raised itself above the horizon for a few minutes and then disappeared again." The lead, or creek of open water, which was then reached, prevented further movement until March 11, when it was frozen and a start became practicable. The depth of the lead was determined by soundings to be 110 fathoms. On March 14 the lead had been passed, and the temperature was -58° (?) F. Two days later Prof. McMillan had to be sent back to Cape Columbia at once on account of frostbite. Sounding gave a depth of 825 fathoms. We were over the Continental Shelf, and as I had surmised, the successive leads crossed in the fifth and sixth marches

composed the big lead and marked the Continental Shelf."

By an admirable system of advance, main and supporting parties, the expedition moved rapidly north, covering no fewer than fifty minutes of latitude (about 57 miles) in three marches. The fourth supporting party started on the back trail from about latitude 88°. and on April 2 Commander Peary, with his party of Eskimos, moved towards the pole.

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In a march of about ten hours the party travelled twenty-five miles and was well beyond the 88th parallel, with the sun now practically horizontal." Several long marches were accomplished, and one of forty miles in twelve hours. In four days, two degrees of latitude were covered, that is, a distance of about 138 miles. On the last stage of the journey Commander Peary's only companion was an Eskimo. An observation made on April 6 showed that the latitude was 89° 57', so that the pole had been praɛ

tically reached. Thirty hours were spent in making observations there and ten miles beyond the camp, and in taking photographs. No land could be seen. The minimum temperature recorded during the thirty hours was 33° and the maximum - 12° (?) F. A sounding was made five miles from the camp, but bottom was not touched at 1500 fathoms. The party returned to Cape Columbia on April 23, and to the Roosevelt four days later. On July 18 the ship left Cape Sheridan and arrived in Indian Harbour on September 6.

The record of the expedition is a triumph for good organisation and persistent endeavour, and though details of the scientific observations are not yet available, the narrative gives good reason for believing that, so far as the time permitted, some valuable work was accomplished. Commander Peary states that Prof. Marvin and Prof. McMillan both secured numerous observations of tidal and meteorological conditions, as well as other data of scientific interest, while Dr. Goodsell gave special attention to microscopic work.

Commander Peary's achievement has rendered unnecessary any further expedition to reach the North Pole, so that attention may now be concentrated upon systematic scientific work in the region of which a preliminary view has just been taken. Whatever may be the ultimate decision as to relative claims to have been the first to reach the pole, there can be no doubt that the work carried on by the members of Commander Peary's expedition will be of greater value to science than mere observations of latitude taken during a dash" to the pole. The success of the expedition is associated, however, with a fatal mishap to one of the scientific members. Prof. R. G. Marvin, of Cornell University, was drowned on April 10, forty-five miles north of Cape Columbia, while returning from latitude 860 N. in command of a supporting party. Prof. Marvin was only thirty years of age, and his death has caused great regret.

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Though Commander Peary refers in his narrative to observations for latitude made at various points, no particulars are given, but that may be because the narrative was written for the general public. The explorer has had a unique experience in Arctic regions, and when his observations are published they will, it is hoped, show that the instruments used and corrections applied enabled him to determine position with reasonable accuracy. The determination of latitude by observations of the sun is, however, very difficult in latitudes near the poles. Without suggesting that Commander Peary's results may be found to require correction, it is of interest to indicate the conditions of observation in polar regions and the instruments used by some explorers.

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LATITUDE OBSERVATIONS IN POLAR REGIONS. To an explorer situated at one of the poles of the earth, the stars and all other heavenly bodies appear to pass round him in circles parallel to the horizon once in twenty-four hours, and the altitude of any one star is the same at whatever time it might be taken, provided the atmospheric conditions remain changed. If an explorer could be at either pole during the winter months, the best proof he could have that he had really reached 90° latitude would be by observatio is of stars. Should he be able to measure the altitude of a star with a theodolite or sextant and artificial horizon, at not less than 35° above the horizon, and repeat his measurement at regular intervals, say, of three hours, during one complete rotation of the earth, and find the altitude to be the same at every observation, he would certainly be at an extremity of the earth's axis. Should time be pressing, instead of this somewhat lengthy opera

tion he could take observations of different stars one after the other around the horizon, and then if, after applying corrections for refraction and instrumental errors, he found in each case the altitude to be the same as the declination of the star given in the Nautical Almanac or similar publication, he could conclude that he was exactly on a pole of the earth. The former of these two would be the more satisfactory method, because effects of refraction, which is very uncertain in high latitudes, would be eliminated. But it is usually daylight when the explorer reaches his highest latitude, and the stars are not visible, so here is a practical difficulty in the way of either of these methods. Still, much the same plan could be followed with the sun. If an explorer is exactly at the pole the sun will pass round him in a circle in twentyfour hours, and the only change in its altitude will be due to the change in declination, which is given in the Nautical Almanac for every hour. Should it be found, then, during a series of observations of the sun extending throughout twenty-four hours, or over a number of hours, that the observations changed just the amount of the sun's change in declination for every hour, the only place where the observer could be would be at the pole.

If, instead of the altitude remaining the same, it should, during one rotation of the earth, be found to decrease for twelve hours and then increase for the other twelve, or vice versa, it is clear that the latitude would not be 90°, but its value could easily be computed from the observations.

As regards observations for time taken at or near the poles, the ordinary method of taking sets of altitude of east and west stars fails altogether, for the simple reason that the altitude remains practically the same at all times, and it is impossible to state the exact instant of time corresponding to a certain altitude. The only satisfactory method of rating a chronometer would be by taking transits of the sun or stars by a theodolite firmly fixed and left in position on a stand. Since all the meridians converge at the poles, there can be no difference of longitude, and another remarkable fact would be that an observer exactly over the North Pole would be facing south whichever way he turned, and this would interfere with his ordinary idea of bearings considerably.

There can be no doubt that the best instrument to take for accurate observations at or near a pole is a good transit theodolite, and altitudes below 30° or so should, if possible, be avoided. With a sextant and artificial horizon, a low altitude, such as 100 or 11° or below, is very satisfactory. In the first place, it is extremely difficult to make a contact at all, and then the image in the artificial horizon is usually greatly distorted, specially when a glass plate artificial horizon is used, silvered only on the back. But whether the observations are taken with a theodolite or sextant and artificial horizon, it is naturally impossible to expect any result that can be depended on unless a solid foundation exists upon which to level up the theodolite or place the artificial horizon.

To take advantage of the best conditions of the ice and ensure a safe return, a polar explorer endeavours to reach his highest latitude at an early date when the sun's declination is only a few degrees. Thus it was April 7, 1895, when Dr. Nansen arrived at 86° 12'3' N., and April 25, 1900, when Captain Cagni, of the Duke of the Abruzzi's expedition, reached latitude 86° 34′ N., his farthest north; whilst the two explorers whose names are just now so prominent both announce that they discovered the North Pole in this month.

Although doubtless unavoidable for the reasons stated, these comparatively early dates of reaching

high latitudes have great disadvantages so far as observations are concerned. The stars have disappeared, to be seen no more for five or six months, and the sun is so near the horizon, owing to its low declination, that the meridian altitude, upon the measurement of which the latitude usually depends, is not high enough to give a satisfactory result, owing to the uncertainties of the refraction correction, and, if a sextant and artificial horizon are used, to the great difficulty in making the observation at such a low altitude, and unavoidable distortion of the sun's image. For good results it is a maxim with geographical surveyors that no altitude should be taken that is less than 250 or 30°.

A meridian altitude of the sun only a little above 6o, which is what would be observed at the poles on April 6, or between 11° and 12°, which would be the amount for April 21, would not be likely to furnish a very exact latitude, even if taken with a first-rate instrument under favourable climatic conditions, much less so when these are not favourable and when the observations are made with the small portable instruments which alone can be carried by the explorer on a rapid dash to the pole, when every ounce of weight is a serious consideration.

Dr. Nansen, after leaving the Fram, took with him on his famous sledge journey a small altazimuth, with 4-inch circles, and a pocket sextant with an arc of 1 inches radius, both of which, by means of verniers, read to single minutes. It was with the pocket sextant, however, that his farthest north latitude observation was made, using the natural horizon, and he admits that the result cannot be depended upon to a minute or two

Captain Cagni observed with a sextant, and in referring to his farthest north latitude, which depended upon an altitude of about 12°, states that he used both the artificial horizon and the natural horizon, which latter was very distinct.

Coming now to the Antarctic regions, Captain Scott's expedition was well provided with instruments, but his highest latitudes on the southern journey were taken with a small theodolite. In the case of this expedition, the dates when the high latitudes were reached were later on in the summer, so that the sun's southern declination, and consequently its meridian altitude, was higher.

This same remark also applies to Mr. Shackleton's recent expedition, for on January 3, when the last observation on his long journey to the south was made, the sun's meridian altitude was about 25° 33', which resulted in a latitude of 87° 22′, the further distance travelled south of this depending for its measurement chiefly on the sledgeometer, which throughout the journey had been found to agree well with the latitudes observed. On his journey Mr. Shackleton used a 3-inch transit theodolite, reading to single minutes, and the adjustment of which had been thoroughly tested. He also had the advantage of observing on terra firma instead of moving ice, so altogether his resulting latitudes doubtless compare very favourably, as regards accuracy, with those of other polar explorers.

As regards the effect of extreme cold on the refraction correction of the altitude, it may be interesting to note that, for an altitude of 11°, there is a difference of just above 1' for a change of temperature from +500

to - 60° F.

Sextant observations taken with a glass plate artificial on moving ice would be most untrustworthy, for, in addition to the probable sources of error already referred to, there may be slow oscillations of the water, tidal or other, that may affect the level of the reflecting surface considerably.

CHEMISTRY IN THE SERVICE OF THE STATE.

1

IT is generally known in chemical circles that Sir Edward Thorpe is relinquishing the post of principal chemist at the Government laboratory, which he has so ably held for the last fifteen years. In the closing paragraphs of the present report he notes that it is the last document of the kind he will have the honour of submitting to the Treasury,, and takes the opportunity of directing attention to the great increase which has occurred in the work of the laboratory during the period in question. It appears that the number of samples examined yearly is now more than double what it was fifteen years ago, the actual figures being 76,513 in the year 1894, and 176,935 in 1908-9.

Naturally there is not much of strictly scientific importance to be found in the record of an establishment devoted to "the daily round, the common task " of acting as chemical Abigail to all and sundry Government offices. Yet in its applications of chemical science to civic requirements Sir Edward's department touches the public welfare at many points; and in illustration of this some gleanings from the pages before us are not. without interest. For statistics, in which the report abounds, the reader may be referred to the publication itself.

The business of the laboratory is subdivided into three main classes. Articles examined for the two great revenue departments, Customs and Excise, form by far the largest number of samples. A considerable amount of work, however, is submitted by other branches of the executive, especially the Board of Agriculture, the India Office, the Admiralty, the Board of Trade, and the Office of Works. Finally, samples, relatively few in number, but important as being objects of dispute in legal proceedings, are referred to the laboratory for examination under the provisions of the Sale of Food and Drugs Act and the Fertilisers and Feeding Stuffs Act.

In its rôle of revenue chemist, the laboratory is required to hold the balance fairly between the Exchequer on the one hand and the maker or importer of taxable commodities on the other. Alcoholic liquors, sugar, tobacco, tea, coffee, and chicory naturally furnish the greater number of samples for analysis, since they are the chief dutiable articles in this country. But in safeguarding the revenue derived from these products it is also necessary to analyse numerous other articles; thus the principal chemist remarks that "the duty on chicory involves the examination of many substances botanically allied to it, such as dandelion and burdock roots." Genuine cider, again, is not liable to import duty, but samples are analysed nevertheless; for "if evidence is found that spirit has been added," the cider comes under the tariff as a preparation containing spirit, and is taxed accordingly. It is noted that a large proportion --more than 13 per cent.-of certain beverages sold as temperance drinks contained an excess of alcohol, the quantity ranging from 3 to 11 per cent. of proof spirit.

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