40 On the Trigonometrical Survey. 
When the two elements of combustion, thus carried up into the 
atmosphere, come into contact, thunder and lightning are pro- 
duced; the light and heat thus generated fly off, and the water, 
which. for med the bases of the two gases, is recomposed, and 
descends to the earth in a shower of hail, rain, or snow. 
Now if we examine the following experiments on water, we 
shall find them exactly similar to those just mentioned ; for the 
same undeviating law which takes place upon the surface of our 
globe, and in the atmosphere that surrounds it, obtains in the, 
laboratory of the chemist. 
When a Leyden jar is discharged a certain number of times 
into a drop of water, this fluid is wholly converted into two gases, 
which are equal in weight to the drop of water. Now, as no- 
thing is present in this experiment, but water and the two ele- 
ments which were>contained in the jar, the two gases are com= 
pounds, consisting of those elements and water. Thermogen, 
the element of heat, converts a portion of the water into an in- 
visible gas: photogen, the element of light, converts the other 
part of the water into another gas; water being the bases of 
the two aérial fluids. The two elements are kept separate by 
their bases; but an electric spark being passed through them, com- 
bustion:is produced, and the bases of the two gases are resolved 
into a drop of water, of the same weight as the two gases; the 
two elements being imponderable. I think it would be wander- 
ing very far from that simplicity which is every where seen in 
the operations of Nature’s laws, to suppose (for it can only be a 
supposition) that the bases of the two gases are not water, but 
two new matters; and when the gases are decomposed, these 
unknown matters are converted into water. 
Lynn, June 30, 1817, EzEKIEL WALKER. 
: [To be continued. ] 
V. Extract of a Letter from Colonel MuncE to WILLIAM 
BrackwooD, Esq. relative to the Trigonometrical Survey*. 
Edinburgh, June 7, 1817 
Sir, I HAVE the honour to inform you, that in consequence of 
the trigonometrical survey, carried on under my direction, having 
been brought on so far into the north as to admit of the descrip- 
tion of the longest meridional line passing through Great Britain, 
M., Biot, under the authority of both the French and English 
Governments,.is arrived in England for the purpose of doing, in 
the several parts of our arc, the same series of experiments that 
had been formerly done by himself and the Commission of the 
Board of Longitude, at Formentera, one of the Balearic Islands 
* From the Edinburgh Monthiy Magazine for June 1817. ’ 
in 
