Catvdnism compared with Electricity. 83 



embraces, which arc, according to my experience, decided- 

 ly erroneous. One of these is, that water dissolves air. An 

 excellent paper of Mr. W. Henry, on the absorption of 

 gases by water, in the Philosophical Transactions for 1 803, 

 has shown us sufficiently in what light we should view the 

 supposed solution of air in water. Certainly air that is re- 

 tained in water by mechanical force, and which always 

 escapes when that force is withdrawn, cannot, with any pro- 

 priety, be said to be held by chemical affinity. 



Dr. Thomson has been misinformed respecting my opi- 

 nions on the expansion of liquids. In vol. i. page 343, he 

 gives it as my suggestion, that all liquids expand the same 

 quantity from their freezing to their boiling temperatures. I 

 never entertained such an opinion ; and it is certainly erro- 

 neous. My idea is, that pure and homogeneous liquids, 

 such as water and mercury, expand according to the square 

 of the temperature from the points at which thev congeal ; 

 but I have not yet found a law to regulate the relative ex- 

 pansions of these and other liquids. 



Manchester, l am ; } T ° urs > &c - 



June 19, 1 004. J. DALTON. 



XVI T. On a distinguishing Property between the Galvanic 

 and Electric Fluids. By Mr. John Cuthbkrtso^. 



To Mr. Tilloch. 



DEAR SIR, 



Oince my letter to Dr. Pearson appeared in your Philoso- 

 phical Magazine for last month, I thought the following 

 additional experiments necessary: 



The two experiments last mentioned in the above letter 

 were compared with common electrical discharges, with a 

 view to prove what quantity of coated glass would be re- 

 quired to take a charge sufficient to ignite the same lengths 

 of wire. 



Two jars, each containing about 1 70 square inches of coat- 

 ing, were set to the conductor of a 24-inch single-plate elec- 

 trical machine, with my universal electrometer loaded with 31 

 grains, (see Nicholson's 4to Journal, pi. xxiii. vol. xi.). 

 "8 inches of the same sort of wire were laid in the circuit :— - 

 57 revolutions of the plate caused the electrometer to dis- 

 charge the jars, which ignited the wire perfectly, as in the oth 

 experiment. In the next place, 6 inches of the wire being 



F 2 Jaid 



