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VI. On a neiv photometer, with its application to determine the 
relative intensities of artificial light, &c. By William 
Ritchie, A. M, Rector of the Academy at Tain. Communicated 
by the President, ‘ • * 
Read December i6, 1824. 
1 . I N a paper which I lately communicated to the Edin- 
burgh Philosophical Journal, I endeavoured to show, that 
caloric flies ofF from the surface of a heated body by the re- 
pulsive energy existing between its own molecules, and con- 
sequently, that their velocity increases with the temperature 
of the body. This conclusion I deduced from the fact, dis- 
covered by Delaroche, that invisible caloric freely permeates 
very thin plates of glass, in the same manner as light, but 
that it is completely intercepted by thicker plates. If the tem- 
perature of the body be raised, the atoms of caloric will be 
brought nearer each other, their repulsive energy augmented, 
their velocity increased, and consequently, they will now find 
their way through a plate of glass which formerly inter- 
cepted them. If the temperature of the body be raised still 
higher, the molecules of caloric will acquire a velocity 
suflicient to permeate the various humours of the eye, 
and produce an impression on the retina, or in other words, 
they will become light. From this view of the subject, 
I was naturally led to the invention of an instrument 
which w’ould be affected by visible caloric or light, wTilst 
