rCRISCOPIC SPECTACLES. 
two of theifluids, most essential in these phenomena, the finid 
which produces heat, and the electric fluid. 
1 consider as a circumstance promising great advantage in 
forwarding experimental philosophy, a correspondence nouf 
established between Mr. Singer and Mr. Haussmann, as these 
two experimental philosophers do not stop on the superficy of 
I the phenomena, but having followed them as deep as the present 
means can permit, they are able to devise new means of explor- 
ing their still < hidden parts, and thus to dispel many errors 
which had crept into natural .philosophy, by hasty and un-* 
warranted conclusions. 
I have no doubt that this favourable change will be seconded 
by Mr. Singer’s ^work, announced in the. same number of your 
Journal as being put to the press, under i the) title of Elements 
ef Electricity and Electro-chemistry j because I know, , by oui 
conversation when Mr. Singer came to Windsor, that he has 
followed these experiments, not only with all the known instru- 
ments, but with many of' bis own invention. 
I have the honour to be. 
Sir, 
Your most obedient, humble servant, 
J. A. DELUC. * 
. . III. 
I 
Letl^erfram JV. H. Jf'Q.llaston, D. Sec.- B,.S. together mth 
n Report of Mons. Biol, off he^ j7uperial t Institute of Frauce^ 
upon Feriscopic, SpeclaUef^ 
. d'o Mr- Nicholson. 
If ; 
. • ... 
i]I N the loyth lunmbcrv>of .your Journal (for February last) 
JE k.yiour correaponileDt'Mn;. Jones .renewed his attack upon tlie 
pei'iscopic construction of spectacles, maintaining, as before, that 
the 
