214 Dr Fyfe mh the Illuminating and Heating Fewer of 



The influence of humidity I believe to be very important in 

 modifying the results. The distribution of moisture as we 

 rise in the atmosphere varies extremely at dififerent seasons. 

 In spring the hills are chilled by continued condensations of 

 moisture, whilst the plains are comparatively dry ; and in 

 autumn the reverse often occurs. I believe that the actual 

 fall of rain on low and high grounds confirms this view, the 

 autumnal rains being often heaviest in the plains, whilst in 

 spring and summer the excess is amongst the hills. '^ 



The curve in Plate II.,t representing the mean daily range 

 for five years, is deduced from careful observations made at 

 Edinburgh by ^Ir Adie, with self-registering instruments. + 



On the Comparative Illuminating and Heating power of dif- 

 ferent kinds of Coal-gas Burners^ and on the use of Coal-gas 

 as a source of Heat. By Andrew Fyfe, M. D., F. R. S.E. 

 Communicated by the Society of Arts. 



I. On the Comparative Illuminating Power of Gas Burners.^ 



It is well known that coal-gas varies in its composition and 

 quality, according to the process followed in its manufacture. 

 After being freed from impurities, it consists chiefly of hydro- 

 gen, carbonic oxide, and different varieties of hydro-carbons. 

 The hydrogen, carbonic oxide, and light hydro-carbons, con- 

 stitute by far the largest proportion ; but it is the heavy hydro- 

 carbons that are the true source of light, for though all of 

 them are inflammable, yet the former give very little light 

 during their combustion. 



* Professor Forbes in a postscript appended to this memoir, adds, " I am 

 glad to find that the reasoning I have employed in page 211, to account for 

 the diurnal variations of the decrease of heat in the atmosphere, is entirely 

 confirmed by the observations of Eschmann, Kaemtz, and Homer in Swit- 

 zerland, recorded in Poggendorf 's Annalen, xxvii. 345, and in Dove's Reperto- 

 rium, iii. 331." Edit. 



t The vertical lines in the plate correspond to the middle of each month. 



X The latter part of this paper has been remodelled since it was read. — 

 Dec. 1839. 



§ Read before the Soeiety of Arts fof Scotland Uth March 1840, 



