Professor Forbes's Researches on Heat. 97 



also peculiarities of colour and appearance of the external 

 envelopes and tails so often referred to, which might be worth 

 examining. 



These remarks have, I trust, thrown some additional light 

 on the nature of gaseous combustion and the influences affect- 

 ing it. The inquiry seems to be worth the prosecuting, in 

 order to obtain accurate results. For this purpose superior 

 apparatus is required: one most essential instrument is a gas 

 reservoir, from which gas can be expelled with any de- 

 gree of force that may be required, and with considerable 

 accuracy. The flask I may also remark, though it may do 

 very well for most flames, does not suit well those which re- 

 quire a large and free supply of the atmospheric gas ; thus 

 olefiant gas will scarcely burn in the flask full of air : it 

 shakes violently as if seeking for air, and then goes out ; and 

 this cannot be remedied by forcing in air, as the agitation 

 thereby produced blows out the flame. By pursuing the in- 

 vestigation with greater accuracy, results may probably be 

 obtained that may assist in elucidating the nature and af- 

 fections of gaseous bodies. In the mean time I shall prosecute 

 the inquiry as much as lies in my power, [with the view of 

 giving greater accuracy to the results already obtained, or 

 making new observations connected with the subject. 



Linlithgow, June 2, 1838. 



XV. Researches on Heat. Third Series. § 1. On the un- 

 equally Polarizable Nature of different Kinds of Heat. 

 § 2. On the Depolarization of Heat. §3. On the Refran- 

 gibility of Heat. By James D. Forbes, Esq., F.R.SS. 

 L. 8^ E.f Professor of Natural Philosophy in the University 

 of Edinburgh.* 



[Illustrated by Plates II. & IV.] 



§ I. On the unequally Polarizable Nature of different Kinds 



of Heat. 

 T has been my anxious wish to preserve these papers pure 

 from even the appearance of controversy, and those who 

 have paid attention to the recent history of our present sub- 

 ject must be aware that without making direct allusion to the 

 doubts which have at different times been thrown upon my 

 experiments, I have contented myself with adducing new facts 

 and more convincing reasonings ; and I have had the satis- 

 faction to see that the general result of this course has been 



* Read before the Royal Society of Edinburgh 16th of Apiil 1838: 

 abridged by the Author from the Transactions of that Society, vol. xiv. j 

 and communicated by him. 



PhiL Mag. S. 3. Vol. 13. No. 80. Aug, 1838. H 



I 



