310 



Mr. G. J. Symons. 



[June 21 r 



That the temperatures observed cannot be absolutely the same is 

 evident ; for there must be a certain excess of pressure in the neigh- 

 bourhood of the surface of the solid in order to produce a flow of 

 vapour from it to the surrounding space ; and consequently the 

 evaporating substance must have a higher temperature corresponding* 

 to this higher pressure. Our results, we venture to think, show that 

 with solids, as with liquids, this difference, even when rapid evaporation 

 is taking place, is an extremely minute one. 



IV. "Note on the Establishment and First Results of Simul- 

 taneous Thermometric and Hygrometric Observations at 

 Heights of 4 and 170 feet, and of Siemens' Electrical Ther- 

 mometer at 260 feet above the ground." By G. J. SYMONS, 

 F.R.S. Received June 6, 1883. 



It is just a century since James Six (the inventor of the well- 

 known Six's registering thermometer) commenced some occasional 

 comparisons of the temperature of the air at the top and bottom 

 of the tower of Canterbury Cathedral. We do not precisely know 

 the position in which the instruments were placed, and, as ther- 

 mometer screens had not then been invented, his observations can 

 only be accepted as approximately correct ; but as the work in which 

 they are recorded is rather scarce, it may be well to give an analysis 

 of the results. The observations were not consecutive, but made at 

 various dates during 1784-92; the lower thermometer was 5 feet, 

 and the upper one 220 feet above the ground. The daily maxima 

 were about 1° warmer at the top during all frosty period ; alike at the 

 top and the bottom when the temperature was between 40° and 

 50°, and lower at the top by from 3° to 5° when the temperature 

 was about 50°. The minima gave analogous but more marked 

 differences. Some very severe frosts occurred while these experiments 

 were in progress, and with bottom temperatures of — 2°*5, +6°, 

 and +6° '5 respectively, the top temperatures were 15°, 17°, and 21°, 

 showing an excess at the top of 17°'5, 11°, and 14°'5. In ordinary 

 weather the excess of the top minima was not so great, but the 

 average excess was 6°, and there was not a single night when it was 

 colder at the top than at the bottom. 



The author is not aware of any further experiments having been 

 made upon this subject in this couutry until 1861, when the Rev. 

 R. Main, F.R.S. , Radclilfe Observer, had a record commenced of a 

 Six's registering thermometer, and dry and wet bulb thermometers 

 placed near the anemometer on the Radclilfe Observatory, Oxford. 

 These instruments were 105 feet above the ground, and were read 



