1882.] Dr. E. Frankland on Climate in Town and Country. 17 



WEEKLY EVENING MEETING, 



Friday, February 10, 1882. 



George Busk, Esq. F.E.S. Treasurer and Vice-President, in the Chair. 



E. Fkankland, Esq. D.C.L. F.R.S. M.B.I. 



Professor of Chemistry in the Normal School of Science, South Kensington 



Museum. 



Climate in Town and Country. 



The speaker began by describing the construction and uses of the 

 instruments with which he had studied the conditions of climate, for 

 many years past, in various parts of Europe. For the determination 

 of sun temperature, he used a thermometer technically known as the 

 blackened bulb in vacuo laid in full sunshine upon a sheet of white 

 paper. The shade or air temperature was measured by an ordinary 

 thermometer with a clear glass bulb and a scale engraved upon the 

 stem. This thermometer was placed upon the same sheet of paper, 

 and was shaded by a small white paper arch which admitted of a free 

 circulation of air around the bulb. 



He then explained the terms " sun temperature," " shade tempera- 

 ture," and " solar intensity." By shade temperature is meant the 

 temperature of free air in full sunshine. Strictly it ought to be 

 ascertained without any shade at all ; for as soon as a shade is 

 produced, conditions are introduced which often entirely baffle the 

 object of the observer. The shade of a parasol has a different tem- 

 perature from the shade of a tree, and this, again, differs widely from 

 that of a house. The temj)erature of the shade of a sheet of tinfoil 

 is quite different from that of a sheet of writing paper. Indeed it 

 may be truly said that every shade has its own peculiar temperature. 

 The following table shows the effect of the area of shade, and of 

 the quality of the shading material : — 



o 



Beneath larch tree 19*5 0. 



„ white parasol 25 • 



„ small white paper arch 35-0 



„ small arch of bright tinfoil 45 • 2 



Thus shade temperatures, measured during If hours of unin- 

 terrupted sunshine in the middle of the day, and within a few yards 

 of the same spot, differed by no less than 25 • 7° C. These observa- 

 tions were, however, made at Pontresina, 5915 feet above sea-level, 

 and so wide a range does not occur at lower altitudes. 



The most effective shading material is, obviously, that which most 

 perfectly reflects solar heat ; and of all materials with which he had 

 experimented white paper was found to be the best, white linen and 



Vol. X. (No. 75.) c 



