TRANSACTIONS OF THE SECTIONS. 4S 



32'', and for the heights 29 and 30 inches of the barometer. The indices i, i, i, seen 

 through these sUts and drawn on the fixed portion of the instrument, are so placed 

 that when the slide is closed they shall point to zero of all these short scales. When 

 the slide is closed the scales C and D should coincide, and the scales A and B should 

 have the correct tabular relation. 



On the other side of the instrument there is another sliding-piece. The scale H 

 on one edge of the sliding-piece is a simple logarithmic scale, the argument in this 

 instance being the degree of humidity, saturation of the air being=l"0. The fixed 

 scale I opposite to this is also logarithmic, and represents the logarithm of the 

 elasticity of vapour ; the argument, however, being the temperature corresponding 

 to the elasticity. 



The scale E on the other edge of this sliding-piece is one of equal parts, and re- 

 presents the temperature of the dew-point. The fixed scale F is the weight in grains 

 of the water in a cubic foot of air corresponding to the temperatures in E. On a 

 line with F is a short scale G, which gives the correction to be applied to the num- 

 bers in F for the depression of the dew-point below the temperature of the air ; the 

 argument being the number of degrees of this depression. An index g is placed so, 

 that when the slide is closed, and the scales E and F are in correct tabular relation, 

 it shall point to zero of scale G. The scales E, F, and G ought in strict accuracy 

 to have been in logarithmic relation to each other; but it was found, on trial of ex- 

 treme cases, that they are already (owing to the laws of change of elasticity) so very 

 nenrly so, that no appreciable error is introduced by 'the approximate method 

 adopted. 



lie use of the instrument will be best understood from an example. Let the dry 

 thermometer read 70°, and the wet 65°, the difference is 5° ; let also the height of 

 the barometer be about 29"5 inches. 



Move the first sliding-piece (B C) until the index i is opposite 5'0 on scale 6 ; look 

 for the division 65°'0 on scale B ; opposite 65 will be found on scale A •561 in. as the 

 elasticity of vapour ; again look for 65° on 0, and opposite to it we shall find on D 

 62*1, which is the temperature of the dew-point. 



These two numbers having been written down we pass to the second slide. Set 

 the point I'O on H to 70° (the temperature of the air) on I ; the dew-point we have 

 found to be 62°' 1 ; find this on I, and opposite to it we find on H -770 as the degree 

 of humidity. 



Again : — ^The depression of the dew-point below the temperature of the air is 8° ; 

 set g to 8° on G, find 62°'l on E, and opposite to it on F we find 6"15 grains as the 

 weight of water in a cubic foot of air at the time of the observation. 



It should be mentioned that the standard scales furnished to Mr. Adie of London, 

 the maker of the instrument, were divided at Kew by myself, with the aid of a 

 dividing engine constructed by M. Perreaux of Paris. 



CHEMISTRY. 



On the Products of the Action of Heat on Animal Substances. 

 By T. Anderson, M.D. 



Dr. Anderson, having discovered picoline in coal-tar, was led to investigate the well- 

 known and peculiar foetid oil called bone- oil, and, to obtain the best results, operated 

 in the last experiment upon 250 gallons of the distilled bone-oil, and discovered at 

 least three different series of bases in the oil. In the first he had established the 

 existence of the bodies called methylamine, ethylamine, butylamine, petinine, and 

 probably others ; in the second series, picoline, and other bodies of which it is the 

 type. The third aeries is veiy remarkable, and all the members of it are characterized 

 by decomposing by heat and excess of acid into bases of the picoline series, and a 

 remarkable and peculiar red or orange-coloured resinous substance. This extensive 

 investigation was not yet concluded ; but the oil, besides these bases, contained ben- 

 zole and the nitriles of some of the fatty acids. 



