and agitated; soon the cloud is seen to approach and join the latter, involving both extremities in one column having a spiral motion, and on it moves or continues stationary. The power of electricity in raising bodies, when combined with this peculiar whirling motion, will account for fish, &c. being carried up in its vortex and afterwards discharged to a distance on the earth. The motion of the dust-storm may be described by spinning a tee-totum on a drop of ink; and the way in which bodies are projected may be in like manner described, by letting fall a drop of ink on the centre of a tee-totum while spinning. In this case the particles of ink are thrown off at tangents ever varying, as the centre moves; and perhaps it will be found, that when these kind of storms pass through forests, trees uprooted are distributed something in this manner. The violent dust-storms are by some supposed to commence at the foot of the hills. I cannot tell if this be the case or not, but should think that they do not necessarily do so, as many often originate in extensive arid plains; and the rarefaction of air, from great and longcontinued heat, may be in some way connected with the exciting cause. Some of them come on with great rapidity, as if at the rate of from 40 to 80 miles an hour. They occur at all hours, oftentimes near sunset. The sky is clear, and not a breath moving; presently a low bank of clouds is seen in the horizon, which you are surprised you did not ob. serve before; a few seconds have passed, and the cloud has half filled the hemisphere and now there is no time to lose-it is a dust-storm, and helter-skelter every one rushes to get into the house in order to escape being caught in it. The electric fluid continues to stream down the conducting wire unremittingly during the continuance of the storm, the sparks oftentimes upwards of an inch in length, and emitting a crackling sound; its intensity varying with the force of the storm, and, as before said, more intense during the gusts. Many dust-storms occur at Lahore and in the Punjaub, generally during the hot and dry months, as many as seven and nine in one month. One that occurred last year in the month of August seemed to have come from the direction of Lica, on the Indus, to the west and by south of Lahore, and to have a north-easterly direction. An officer travelling, and at the distance of twenty miles or so from Lica, was suddenly caught in it; his tent was blown away, and he himself knocked down and nearly suffocated by the sand. He stated to me that he was informed by one resident at Lica, that so great was its force at the latter place, as to crack the walls of a substantial brick dwelling in which the above officer had lately resided, and to uproot some trees about. The instant the insulated wire is involved in the electric current marked by the column of dust, down streams the electricity. I have sometimes attempted to test the kind of electricity, and find that it is not invariably in the same state; sometimes appearing +, at other times, and changing during the storm. One day I caused the current to pass through a solution of cyanide of silver, so as to affect a small piece of copper, which was rapidly covered with a coating of silver, which upon drying peeled off. In this case the cyanide of silver was pure, without any salt; but in subsequent attempts to silver a wire in this way, I have not succeeded, only a very slight deposit taking place, which was not increased by long exposure to the influence. But in all the cases I tried subsequent to the one first alluded to, the oxide of silver was dissolved in cyanide of potassium. In the course of time bright and minute crystals were formed, transparent and colourless, on a copper Yours truly, coin. P. BADDELEY, Arty. Surgeon, Lahore. Tables for determining Heights by the Barometer. Computed by Major J. C. HANNYNGTON, B. N. I. These tables are so framed as to bring the logarithmic process into a purely arithmetical and very simple form. They are to be used as follows: Rule. Correct the Barometer at the colder station, by adding the correction from Table I. for the difference of temperature. Extract the Barometric. Factors from Table II., then according as the Barometer at the lower station is more or less than 30 inches, multiply the sum or difference of these Factors, by the Factor for the sum of the temperatures from Table III. The result will be the difference of altitude in feet. Where great accuracy is desired a small correction for the approximate Latitude of the place may be applied from Table IV. This is to be added to or taken from the computed height, according as the Latitude is less or more than 45°. Sum of Thermometer 163°. Factor from Table III. 66.98 24896 28008 18672 18672 Product, Hazaribagh above Calcutta, in feet, 2084.4176 Here it will be observed that the Barometer at the lower station exceeds 30 inches; therefore the sum of the Barometric Factors is used. The Latitude of Hazaribagh being 24° and the elevation 2000 feet, it appears from Table IV. that 3 feet may be added to the above result. Sum of Thermometers 94°. Factor Tab. III. Product, difference of altitude in feet,...... 2320.4156 Here the Barometer at the lower station is less than 30 inches, therefore the difference of the Barometric Factors is used. The Latitude being 55° it appears from Table IV., that 2 feet may be subtracted from the above result. Note on the construction of the Tables. Let T and T' be the temperatures of the mercury; t and t' those of the air, h and h' the heights (after reduction by Tab. I.) of the Barometers, at the lower and upper stations, and the latitude of the place. Also let H express inches of the Barometrical column generally; then, T T 9600 Table I. H being the correction of the Barometer for the expansion or contraction of mercury, depending on temperature. Which correction, being applied to the colder Barometer, is additive. Table II. 1000 (209 30-209 H), and consequently the sum or difference of the tabular quantities taken for h and h' is equivalent to 1000 (209 h-209 h'); five figure logarithms being used. TABLE I.-Correction of the Barometer for temperature. Barometer Inches. Difference of the 14 15 16 17 18 19 | 20 | 21 | 2 22 Thermometers. Difference of the Correction to be added to the colder or subtracted 1.000 012345678 9 10 11 12 13 14 15 0 .000 .000 .000 .000 .000 .000 .000 .000 .000 1 .001.002 .002 .002 1.002 .002 .002.002.002 2003 .003 .003 .004 .004 .004 .004 .004 .005 3.004.005 .005 .005 .006 .006.006 .007 .007 4.006 .006.007 .007 .008 .008 .008 .009 .009 5.007 .008 .008 .009 .009 .010 .010 .011 .011 6.009.009 .010 .011 .011 .012.012 .013.014 7.010.011 .012 .012.013 .014.015 .015 .016 8.012 .013 .013 .014 .015 .016 .017 .017 .018 9.013.014 .015 .016.017 .018 .019 .020.021 10 .015 .016 .017 .018 .019 .020 .021 .022 .023 11.016 .017 .018 .019 .021 .022 .023 .024 .025 12.017.019 .020 .021 .023 .024 .025 .026.027 13.019.020 .022 .023 .024 .026 .027 .028 .030 14.020.022 .023 .025 .026 .028 .029 .031 .032 15.022 .023 .025 .027 .028 .030 .031 .033 .034 16.023 .025 .027 .028 .030.032 .033 .035 .036 17.025 .027 .028 .030 .032 .034 .035 .037 .039 18.026.028.030 .032 .034 .036.037 .039 .042 19.028.030.032 .034 .036 .038 .040 .042 .044 20.029 .031.033 .035 .038 .040 .042.044 .046 21.031 .033 .035 .037 .039 .042 .044 .046 .048 22.032 .034 .037.039 .041 .044 .046 .048 .050 23.034.036 .038 .041 .043 .046 .048 .050 .053 24.035 .038 .040 .042 .045 .048 .050 .052 .055 25.036.039 .042 .044 .047 .049 .052 .055 .057 26.038.041 .043 .046 .049 .051 .054 .057 .060 27.039 .042 .045 .048 .051 .053 .056 .059 .062 28.041.044 .047 .050 .053 .055 .058 .061 .064 29.042 .045 .048 .051 .054 .057.060.063 .066 29 16 17 18 19 20 21 22 23 24 25 26 27 28 |