*Nahinch, L., co. Tipperary. Ibid., vol. ix. Naneevin, L., co. Galway. Ooney, L., co. Monaghan. Owel, L., co. Westmeath. Pad or Boat, L., co. Fermanagh. *Ravel, L., co. Antrim. Ibid., vol. vii.; Journ. R. H. A. Association, 2nd S., vols. iii. and iv., 3rd S., vol. i., and 4th S., vol. ii. *Rohan's, L., co. Monaghan. Ibid. *Ramor, L., co. Cavan. Ibid., 4th S., vol. vii. Scur, L. (2 crannogs), co. Leitrim. St. John's, L. (4 crannogs), co. Leitrim. Talogh, L. (several crannogs), co. Leitrim. *The Miracles, co. Fermanagh. Journ. R. H. A. Association, 4th S., vols. ii. and v. Toome Bar, co. Antrim. Ibid., N.S. vol. v. *Tully, L. (3 crannogs), co. Cavan. Ibid., 4th S., vol. vii. Tullyline, co. Cavan. Veagh, L., co. Donegal. Williamstown, L., co Galway. Ibid., 5th S., vol. i. p. 337. Several reports on prehistoric objects have been promised by scientific observers in various parts of the country, and your Committee urge that no more delay should be made in presenting them than is compatible with accuracy and thoroughness. It is requested that the Committee be reappointed as before without grant. Fourth and Final Report of the Committee, consisting of the Hon. RALPH ABERCROMBY, Dr. A. BUCHAN, Mr. J. Y. BUCHANAN, Mr. J. WILLIS BUND, Professor CHRYSTAL, Mr. D. CUNNINGHAM, Professor FITZGERALD, Dr. H. R. MILL (Secretary), Dr. JOHN MURRAY (Chairman), Mr. ISAAC ROBERTS, Dr. H. C. SORBY, and the Rev. C. J. STEWARD, appointed to arrange an investigation of the Seasonal Variations of Temperature in Lakes, Rivers, and Estuaries in various parts of the United Kingdom in co-operation with the local societies represented on the Association. (Drawn up by Dr. H. R. MILL.) [PLATE XV.] AT the meeting of 1890 this Committee requested reappointment with a grant of 501. in order to draw up a final report on the work inaugurated at its suggestion and carried on by observers, most of whom acted under the auspices of local scientific societies represented on the Association. It was proposed to include in the final report a quantity of material of great value bearing on the seasonal and diurnal variation of river- and sea-temperature accumulated by the Scottish Meteorological Society and still unpublished, and, in addition, to give a general discussion (supported by recent publications of observations in the 'Reports of the Fishery Board for Scotland' and other journals) of the whole question of the variation of temperature in exposed bodies of water as determined by season, actual meteorological conditions, tidal influence, &c. The grant of 201. which was given to the Committee on its reappointment was quite inadequate to pay the working expenses of the scheme and admit of employing a competent person to tabulate and compute means of the great mass of available material. It was accordingly resolved to confine the scope of this report to an account of the observations made on the direct initiative of the Committee, and to the statement of such brief summaries as might be supplied in tabular form by previous observers. The main object held in view by members of this Committee from its first appointment, viz. to produce an authoritative and exhaustive memoir on the seasonal variations of temperature in the lakes, rivers, and estuaries of the British Islands had to be abandoned. At the close of its four years of existence the Committee can only claim to add some additional data to the store awaiting future discussion. This addition is of considerable scientific value, and casts light on several problems in the régime of lakes and rivers. The obser vations have, however, led directly to another and perhaps even more beneficial result. Great interest was taken by the Conference of Delegates from local societies in the establishment of observations in their own neighbourhood. The consciousness that they were engaged in collecting data for a special and definite purpose has stimulated many of the observers to a more earnest study of science, and done something to forward that spirit of fellowship amongst all scientific workers which for the last few years the Association has been so successfully advancing by means of the annual conferences. The results of this stimulus may, it is hoped, continue even when the observations which produced it have ceased. The three previous reports of the Committee may be referred to for particulars as to the method of working, the instruments employed, and the period over which the observations extended; a comparatively small number were continued into the year 1891. The first report was mainly preliminary. The observations it records were upon rivers in Scotland, and although several of the observers have continued their work, most contented themselves with the record of a few months only. The second report 2 notes a large accession of observers on the rivers of England and of Ireland, and as an appendix the directions to observers are reprinted, showing the conditions in which it was desirable that all the observations should be made. In 1889 the reappointment of the Committee was not accompanied by a grant of money, and the observations in that year consequently suffered to a certain extent. The third report 3 gives an epitome of the material collected by the Committee, which forms the basis of the present discussion. The three previous reports, it will be noticed, deal exclusively with the organisation and extent of the observations, none of the data being recorded or discussed in them. 6 Some of the sets of observations have been published in detail. Of these the most important is that accumulated by Dr. Sorby during the years 1884-1888 on the estuaries of the south-east of England, which appeared in the Scottish Geographical Magazine' for 1889 (vol. v. p. 589). An abstract of the results is included in the present report. Observations on the River Thurso, by Mr. John Gunn and others, were 3 Ibid. 1890, p. 92. 1 B.A. Reports, 1888, p. 326. 2 Ibid. 1889, p. 44. printed in the 'Journal' of the Scottish Meteorological Society for 1888. The observations of Mr. W. Watts on behalf of the Manchester Geological Society at the Piethorn and Denshaw Reservoirs have been printed in full in the 'Transactions' of that Society. Mr. Ashworth's observations on the Cowm and Spring Mill Reservoirs have also been published in a summarised form with detailed curves in the 'Proceedings' of the Rochdale Literary and Scientific Society. In addition to the observations specially made or discussed for the Committee, many papers are to be found in the 'Proceedings' of the Royal Society of Edinburgh, the publications of the Meteorological Societies, in the annual reports of the Fishery Board for Scotland from 1887 onward, and in the Scottish Geographical Magazine.' A fuil discussion by Dr. H. R. Mill of very detailed temperature observations made by the staff of the Scottish Marine Station on the Clyde Sea area is nearly completed, and will be presented to the Royal Society of Edinburgh. The best method of publishing the results of the observations dealt with in this report has been carefully considered. There are peculiar difficulties in dealing with a mass of data compiled by observers, some of whom are skilled and others uninstructed in their work, especially when -as in this case-the observations are taken with regularity in few cases and often at different hours. The record of actual observations will be preserved by the secretary of the Committee, who will be glad at any time to place it at the disposal of any one interested in this branch of meteorology. Weekly means have been calculated for each of the stations where reasonably regular observations were made, and these are published in the form of curves in this report. The curve-form was chosen in preference to printing the figures, on account of the much more vivid impression conveyed by inspection as to the relative air- and water-temperatures and their seasonal variations. The unit of the curve is the weekly mean, as in many cases on one or more days of the week the observations were omitted, and a curve of actual daily readings would present a very broken appearance, besides throwing into undue prominence purely temporary variations. The monthly means are given in tabular form. The monthly means are usually calculated as the average of the four or five weekly periods comprised in the month; but in the case of very regular observations the monthly mean is given as the average of the daily readings. Comparison of the two methods shows practically identical results in the case of regular observations, and where the observations are irregular the method adopted for general use obviously gives more satisfactory results. On account of the much greater difficulty of measuring the temperature of air, less reliance must be placed on that part of the work than on the temperature of the water, which is easily found in a readily comparable manner. For the drawing of most of these curves and the calculation of the means from them the Committee has to acknowledge the assistance of Mr. John Gunn, F.R.S.G.S. In several instances, when the observations were carried on by skilled meteorologists in conjunction with the routine of a meteorological station, the observers accompanied their records with a short summary and discussion, in which the most striking relations of temperature were pointed out. These statements, either completely or in abstract, are embodied in this report. A. Observations not recorded in full in this Report. These observations were, as a rule, made by skilled observers for special purposes, and the abstracts were prepared specially for this report by the investigators, to whom the thanks of the Committee are very cordially given. RIVER CHERWELL AT OXFORD. Observations of the temperature of the Cherwell have been made regularly every morning since 1878 by Mr. Edward Chapman, M.A., F.L.S., of Magdalen College, Oxford. The ordinary meteorological observations having been made at the same time, make it possible to compare river-temperature, air-temperature, and rainfall. The rivertemperature recorded below is the mean of daily observations at 9 A.M., the air-temperature is the mean of the maximum and minimum thermometer in the shade for the previous twenty-four hours, and the rainfall is the amount in inches which fell in the previous twenty-four hours. The length of this series of observations gives it peculiar value in affording an indication of average conditions. The average air-temperature for the ten years was 48°9, the average water-temperature at 9 A.M. 50° 3, or 1°4 warmer than the air; the mean annual rainfall for these years being 24.79 inches. The average monthly means are shown in the Curve below. The year of lowest air-temperature was 1887, with 47°.6, the average water-temperature for that year being 49°.8 and the rainfall 18.78 inches, very exceptionally low. The lowest mean water-temperature was in 1888, 49° 0, when the mean air-temperature was 47°.9 and the rainfall 27.39. The highest air-temperature was 50°.9, the mean of 1884, when the water-temperature was also highest, 51° 5, nd the rainfall was 19.48 inches. In 1890, the year of lowest rainfall, when only 17.02 inches fell, the temperatures of air and water were almost at their average (49°.0 and 50°.8 respectively); while in 1886, which was the wettest year, with 32-12 inches of rain, the air-temperature was also normal (49°.0), but the water-temperature was nearly a degree below the average (49° 5). The difference between the average temperature of the warmest and coldest year recorded was only 2°.5 for the water. The highest mean temperature of the water for any month was 68°.7 in July 1887, the month of highest air-temperature also, with an abnormally low rainfall, but in a year the temperature of which was below the average. The lowest mean temperature of the water was 32°.4 for January 1891 (air 32°-6), but the lowest air-temperature was 29°-2 for December 1890 when the water had a mean of 33°-3. The difference in average temperature of water for the same month in different years was greatest in the months of annual maxima and minima. The hottest June was 10° 6 warmer than the coolest June; the warmest January was 90.7 warmer than the coldest January. At the time of annual average temperature the difference was least; thus the warmest April was only 5°6 and the warmest September only 4°.2 above the temperature of the coldest month of the same name. On the average, as shown in Curve XXX., the air-temperature came nearest the water-temperature in the winter months, notably in November and January, when they almost coincided (difference 0°.2), and the two temperatures diverged most in the summer months, particularly April, May, and July, when the difference averaged 2°.3. During the ten years of observation the average monthly air-temperature was higher than the average monthly water-temperature at 9 A.M. on 17 occasions. Of these 6 occurred in January, 2 in February, 4 in November, and 2 in December, or 14 in the winter months; 1 was in March, 1 in May, and 1 in October. In no April, June, July, August, or September, between 1882 and 1891, has there been an instance of air being warmer than water on the average of a whole month. Of course, in the remarkably fine observations now recorded the comparison is made between average air-temperature for the whole 24 hours, and average water-temperature at 9 A.M. only, while in the short series of observations specially made for the Committee the airand water-temperature are both calculated for 9 a.m. Mean Monthly Observations on the Temperature of the River Cherwell at Oxford. By Mr. EDWARD CHAPMAN, Magdalen College. |