54 REPORT — 1869. 



on the cumulative principle for recordiug the mean -values of the difference between 

 the wet- and dry-bulb thermometers, and a self-registering maximum and minimum 

 hygrometer. The author now produced an improved form of the former instru- 

 ment, and a series of curves sho-ning the comparative results of Leslie's hygrometer, 

 his maximum and minimum differential, and his mean self-registering, which may 

 be regarded as the standard ; also the curve of evaporation of water in an open 

 vessel. 



It wiU be seen that these curves differ veiy widely as regards each period of 

 24 hours, but their monthly means are sufficiently imiform to show the approxi- 

 mate accm'acy of the old methods during a long continuance of observations. This 

 is still more evident from the second table, which extends over the greater portion 

 of two years. The author briefly repeats that the action of the 7nean self-register- 

 ing hj'grometer depends upon the condensation of the vapour of alcohol in the wet 

 bulb, tlie readings being taken from the fall of the column of spirit in the tube 

 which represents the drj^ bulb in Leslie's hygrometer. If the temperature of both 

 is alike there will, of course, be no action ; if a uniform dift'erence, say of 5°rahr. , that 

 figure will be indicated on the scale ; and if there is a fluctuating difference, say of 

 from 0° to 10°, dming the period which has elapsed since the last observation, then 

 the record will be 5°, or such other flgure as shall be the sum of the diflerences. 



The author has applied this principle to the recording of the aggregate dif- 

 ference of solar heat in sun and shade, and to the dm'ation of rain (the wet 

 bulb being supplied by a funnel into which the rain is received), and to the 

 amount of nocturnal radiation. He also proposes to apply it, in conjunction with 

 an evaporating vessel, to the recording of mean temperature. .Vise as an anemo- 

 meter, by deducting the results due both to heat and hygrometrical action. 



On CJiamhered Sj>irit-lcveh. By T. "Waenek. 



On a Self-settinrf Type Machine for recoril'mg tlie Hourly Horizontal Motion 

 of Air. By C. J. Woodwaed, B.Sc. 



The author referred in the first place to the methods in use for recording the 

 horizontal motion of air. With a view of testing the errors incidental to the 

 method adopted in the Birmingham instrument, ho had had a series of readings 

 made by two independent observers, and he foimd that during the fifteen days over 

 which the observations extended, there were eighty-five differences of reading. 

 Errors, too, were liable to creep in when the first results were copied into the log- 

 book. To avoid these errors and with a view of obtaining the results in a neat 

 form, the author proposed a mechanical arangement in connexion wath the cups of 

 an ordinary Robinson's instrument, by which a series of type-wheels should be 

 acted upon so as to indicate the hourly horizontal motion of air. From these types 

 the results could be printed off into the log-book. The mechanical details of the 

 contrivance were in a great measm-e due to ]Mr. Alfred Uresswell. 



A model to indicate the principle of the instrument was exhibited. 



CHEMISTET. 



Address by H. Debus, Ph.D., F.B.S., President of the Section. 



I BELiK^n-: it has been the custom with many of my predecessors in this office to 

 place before the members of the British Association a Report of the progress of 

 Chemistry dming the year preceding their elecrion. In attempting to follow 

 their example, I soon found that it would be impossible for me, without making 

 too great a demand upon yom- time, to give even a bare outline of the more import- 

 ant chemical work done during the year. A science the report of whose yearly 

 advances fills about 1000 large octavo pages cannot by any powers of mine have 

 its progress chronicled in an address of half an hour's duration. The best course 



