1813.] Philosophical Transactions, Part IL 1812, 211 



Acid. 



The solid compound of .... 100 -f- 24*89 ammonia, 



llie first liquid 100 + 24-89 x 2 = 49-78 



The second liquid 100 + 24-89 x 3 = 74 67 



If the analyses contained in this paper be near approximations 

 to the truth, it would seem that the weight of a particle of fluoric 

 acid is only 4-5, that of a particle of fluoboracic acid 25*7? which 

 gives us 21*2 for the weight of a particle of boracic acid. The 

 weight of an atom of silica would be 7'46, supposing silicated 

 fluoric acid gas to be composed of one atom of acid, and one 

 atom of silica. But a greater number of results would be neces- 

 sary before any great dependance could be placed on their 

 numbers. 



XIX. On a Psriscopic Camera Olscura and Microscope. By 

 William Hyde Wollaston, M.D. Sec. R.S.] This paper con- 

 tains an account of an ingenious improvement of the camera ob- 

 scura by Dr. Wollaston, whose mechanical inventions of differ- 

 ent kinds have been of so much service, not only to science but 

 to mankind in general. The fault' of the camera obscura is the 

 want of distinctness in the images towards the margin of the field, 

 owing to the figure of the glass, which is usually a double convex 

 lense. Dr. Wollaston removes this defect, at least in a very con- 

 siderable degree, by substituting a meniscus concave towards the 

 objects, and convex towards the eye of the spectator. This is 

 placed at a certain distance within the camera, and the light is 

 allowed to enter by a round hole, which regulates in measiu e the 

 extent of the field of vision, and the quantity of light introduced. 

 His improvement of the common simple microscope, consists in 

 placing a piece of metal with a hole in it between two plano-convex 

 glasses ground to the same axis. This admits a much greater 

 opening, without preventing distinct vision^ and of course more 

 than compensates the diminution of light arising from the con- 

 struction of the instrument. By making the upper surface of 

 the quadrangular prism, which serves to reflect the image of the 

 object in the camera lucida, convex, that instrument becomes 

 capable of giving a more correct image of a considerable field 

 than was before the case. 



XX. Further Experiments and Olservations on the Influence 

 of the Brain in the Generation of Animal Heat. By B. C. 

 Brodie, Esq. F.R.S.] The result of Mr. Brodie's previous ex- 

 periments, an account of which was given in the first number of 

 this Journal, was that animal heat depends upon the functions of 

 the brain, and that when these functions are destroyed, though 

 respiration be kept up as usual, and though the air inspired under- 

 goes the usual chemical changes, yet the temperature of the ani- 

 mal diminishes more rapidly than it would do if respiration were 

 not kept up at all. Before this conclusion could be admitted, it 



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