1820.] Physical Science during the Year 1819. 7 



needles had been placed nearly in the magnetic meridian, a cer- 

 tain temperature preserved for a certain time may be conceived 

 to be capable of inducing permanent magnetism. Probably the 

 red ray failed of this eifect by inducing too high a temperature. 



III. Heat. 



No great quantity of additional matter respecting heat has 

 been brought into view during tfiie course of the last year ; yet 

 there is a very extensive field in this department of chemistry 

 quite open to a judicious experimenter. The facts upon which 

 our opinions respecting heat are founded remain still in a very 

 loose and unsettled state. An accurate set of experiments upon 

 bodies as conductors of heat, upon their specific heat, their 

 latent heat, and the temperature at which they change their state, 

 would set the whole subject in a new point of view, and might 

 even furnish us with some useful data towards resolving the lon^ 

 agitated and still unanswered question, whether heat be a sub- 

 stance or a property. Petit and Dulong seem to have taken up 

 the subject in this judicious point of view, and we have reason to 

 expect much valuable information from a continuance of their 

 experiments ; but 1 am not aware of any new paper on the sjib- 

 ject which they have published since the historical sketch of 

 last year was written. 



The most remarkable paper on this subject which I have seen 

 is an early production of Prof. Leslie, entitled " On Heat and 

 Chniate," which had been read at two meetings of the Royal 

 Society as far back as the year 1793 ; but which was published 

 for the first time in the Annah of Philosophy, vol. xiv. p. 5. 

 The novelty of the matter contained in this paper, its total devia- 

 tion from the opinions at that time generally received, and the 

 originality of the reasoning, and the disregard of authority 

 evinced by the author, appear to have startled the committee of 

 the Royal Society, and prevented them from inserting it in their 

 Transactions. 1 think this decision is to be regretted. It 

 obviously tended to retard the progress of the investigation of 

 heat ; though as far as Mr. Leslie was concerned, it had a favour- 

 able effect. It induced him to reconsider the subject, and pro- 

 bably led to most of the investigations afterwards published in 

 his " Inquiry into the Nature and Propagation of Heat," a 

 publication which has raised the author to so high a rank as an 

 original thinker and discoverer. 



It will not be expected that I should enter into a minute ana- 

 lysis of this curious paper. It obviously contains many of the 

 opinions afterwards brought forward in the " Inquiry," and 

 shows us that the author's notions respecting heat had been 

 taken up at a very early period. Heat he considers as only light 

 fixed in bodies. It is incapable of radiating from bodies witli- 

 out being again converted into light. It only moves by conduc- 

 tion. Hence, in his opinion, if a hot body could be placed in a 



