40S Memoranda respecting Experimenls to ascertain 



As the tliermonietcr used in making these experiments vvai 

 of quite a different kind from any of those in common use, it 

 does not appear possible, at present, to make tlie least compari- 

 son of them together. •* Had the author been aware of the ne- 

 cessity of doing this, it might perhaps have been effected by ob- 

 serving what degree of warmth communicated very slowly would 

 ])rodace a certain alteration in each ; as the standard of com- 

 juirison being thus once made, would serve at any future period 

 for reducing the terms of the one to those of the other. 



The chfJerencein the results of these experiments and those 

 of Dr. Hersche!, it n)ust be acknowledged, is very great; and 

 perhaps may require some further acquaintance with the laws 

 of Nature, before they can he reconciled. According to the very 

 iiilercsting experiments of the latter gentleman, the greatest heat 

 was found to be beyond the coloured spectrum, and on the red 

 side. In these experiments the greatest degree of heat was 

 obtained from the yellow orange rays; and next to that from 

 tliered: then from the orange; next to that from the green: 

 and least of all from the violet. The prism which he used was 

 different from that used by Dr. Herschel and others, as it had 

 jts refringent angle 45^^ instead of 60^. At first sight this 

 does not appear to be a sufficient cause for so wide a difference 

 in the results; and yet, if both are correct, there must be some 

 rational mode of accounting for their discrepancy, depending upon 

 .■scientific and satisfactory principles. In these experiments the 

 Abbe caused the rays to pass through a lens ; and if we refer to 

 the figure of his apparatus, which held the air thermometer, wc 

 shall immediately perceive that the rays had then to pass thicugii 

 the glass of winch the bent tube u'as made: and probably through- 

 the outer cylindrical glass receiver, that held the fluid for the pur- 

 pose of keeping it of an uniform temperature. These tubes be- 

 ing nearly of a cylindrical shape, t!ie rays, by not always im- 

 pinging upon them in precisely the same, or in a proper man- 

 ner, miglit be refracted in a ditfcrent angle from that in which 

 they quitted the prism, and thereby have their nature cl.3;iged, 

 and consequently the degree of warmth might on that account 

 be found different from what it has since been determined. 



Many objections may certainly be made against the mode in 

 which he has conducted these experiments; and indeed they are 

 very candidly stated by himself m'liis account of them; for he 

 says, that although he took all possible precautions, that de- 

 ]iended on himself, to ensure their success, yet he was still very 

 far from being satisfied witli his lal)our. All that can therefore 

 he done, until the diffictdty of reconciling them with others has 

 been removed, is to state the Abbe's just claim to the discovery, 

 that a different degree of heat is produced by the absorption of 



the 



