84 Mr. J. Gill on the Dynamical Theory of Heat. 



a hot object placed in hydrogen is really touched 3*8 times as 

 frequently as it would be if placed in air, and 4 times as 

 frequently as it would be if placed in an atmosphere of oxygen 

 gas. Dalton had already ascribed this peculiarity of hydrogen 

 to the high " mobility" of that gas. The same molecular pro- 

 perty of hydrogen recommends the application of that gas in 

 the air-engine, where the object is to alternately heat and cool a 

 confined volume of gas with rapidity. 



XVI. On the Dynamical Theory of Heat. 

 By Joseph Gill, Esq. 



To John Tyndall, Esq., F.R.S. fyc. 

 Sir, 



THE kind courtesy with which you received my letter " On 

 the Dynamical Theory of Heat," inserted in the Philoso- 

 phical Magazine for August last, encourages me to hope that 

 you will be so good as to give to the following remarks, in con- 

 tinuation of the subject, an opportunity of meeting the notice of 

 scientific men through the same channel. My only object is to 

 elicit truth. I have neither time nor inclination nor ability for 

 scientific controversy, and I long shrunk back from the idea of 

 making public the results of my researches on a subject to which 

 I have given much attention during a large portion of the term 

 of a medium lifetime ; but at length my conviction of the truth 

 of some of the glimpses of light which have been afforded me in 

 these intricate researches forced itself into utterance ; and my 

 anxiety to see the difficulties which, have baffled me removed by 

 abler hands has caused me to persevere in the effort to induce 

 some one of the eminent men who have distinguished themselves 

 in the development of the new science of thermo-dynamics to 

 reconsider these knotty points, and clear away if possible, once 

 for all, the doubts and obscurity which still cloud some parts of 

 the subject. 



Since the date of my last letter I have read your excellent 

 u Lectures on Heat as a mode of Motion," and I feel that the 

 highest praise is due to the ability with which the subject has 

 been divested of technical and mathematical intricacies, and 

 brought within the grasp of mind of every earnest reader of 

 average intellect. By thus exhibiting the results of deep and 

 involved researches in " that simple form in which great truths 

 present themselves to those who thoroughly understand them," 

 an inestimable boon is conferred on numerous readers possessing 

 a knowledge of physics quite sufficient to handle subjects fairly 

 within the range of physical reasoning, though wanting the ma- 



