504 Prof. Wheatstone on the Physiology of Vision. 



applying. Subtracting 4°, however, on this account, we obtain 

 33553° as the quantity of heat absorbed during the electrolysis 

 of water, which ought therefore to be equal to the quantity of 

 heat evolved by the combustion of a gramme of hydrogen gas. 



8. By the inverse method of electrical currents, then, we have 

 found that the quantities of heat evolved by the combustion of 

 copper, zinc and hydrogen, are respectively 594°, 1185°, and 

 33553°. These quantities agree so well with the results ob- 

 tained by Dulong, that I think I may assume that the principles 

 admitted in this paper are demonstrated sufficiently to justify 

 me in making them the basis of a few concluding observations. 



The fact that the heat evolved in a given time by a metallic 

 wire is proportional to the square of the quantity of transmitted 

 electricity, proves that the action of the current is of a strictly 

 mechanical character ; for the force exerted by a fluid impinging 

 against a solid body obeys the same law. Now I have shown in 

 previous papers*, that when the temperature of a gramme of water 

 is increased by 1° Centigrade, a quantity of vis viva is commu- 

 nicated to its particles equal to that acquired by a weight of 448 

 grammes after falling from the perpendicular height of one metre. 

 Hence the mechanical force of a voltaic pile may be calculated 

 from the heat which it evolves. 



Hence also may the absolute force with which bodies enter 

 into chemical combination be estimated by the quantity of heat 

 evolved. Thus, from the data aheady given, the vis viva deve- 

 loped by the combustion of a gramme of copper, a gramme of 

 zinc, and a gramme of hydrogen, will be respectively equivalent 

 to the vis viva possessed by weights of 266112, 530880, and 

 15031744 grammes, after falling from the perpendicular height 

 of one metre. 



LXX. The Bakerian Lecture. — Contributions to the Physiology of 

 Vision. — Part the Second. On some remarkable, and hitherto 

 unobserved, Phanomena of Binocular Vision {continued). By 

 Charles Wheatstone, F.R.S., Professor of Experimental 

 Philosophy in King's College, London f. 

 [With a Plate.] 

 §17. 



IN § 3. of the first part of my " Contributions to the Physio- 

 logy of Vision," published in the Philosophical Transactions 

 for 1838 J, speaking of the stereoscope, I stated, "The pictures 

 * Philosophical Magazine, S. 3. vol. xxvii. p. 206. 



t From the Philosophical Transactions for 1852, part i.j having heen 

 received and read by the Royal Society January 15, 1852. 

 % Reprinted in our April Number. — Ed. Phil. May. 



