136 • A nali/ses of Books, [A u (i . 



" The globules in the nervous fibre being smaller than in the 

 muscular, oversets Monro's theory of theirljeing the same ; but 

 that both authors, with means so very inadequate to those em- 

 ployed by Mr. Bauer, should have made such approaches to the 

 truth, is highly creditable to them, and must prove highly satis- 

 factory to Mr. Bauer, as well as to the public." 



VI. An Account of the Heat of July, 1825; together with 

 some Remarks upon sensible Cold ; by \v . Heberden, MD. FRS. 



Some particulars of this communication will be found in the 

 Annals for February last, p. 138 ; and we subjoin the remarks on 

 the estimation of sensible cold with which the paper concludes. 



'' I am tempted to add to the above some other observations, 

 which, if they are not immediately connected, are not entirely 

 unconnected with this subject ; for it cannot have escaped the 

 attention of any person moderately conversant with natural phi- 

 losophy, that tlie index of a thermometer is a very imperfect 

 measure of what I may call the sensible cold, that is, of the 

 degree of cold perceptible to the human body in its ordinaiy 

 exposure to the atmosphere. For while the thermometer truly 

 marks the temperature of the medium in which it is placed, the 

 sensations of the body depend altogether upon the rapidity with 

 which its own heat is carried off. And this is by no means 

 confined to the actual temperature of the air ; but whatever 

 alteration of quality increases its power of conducting heat ; 

 and, above all, whatever currents increase the succession of its 

 particles in contact with the body, the same will increase the 

 sensation of cold. Hence it is, that in very hot weather, the 

 same stream of air which would heat a chamber, will never- 

 theless be cool to the feeling ; on the other hand, when the 

 thermometer was more than 8(J° below the freezing point. Cap- 

 tain Parry observed, that while the air was still, the cold was 

 borne without inconvenience. 



" It therefore occurred to me, that the proper way to estimate 

 the sensible cold, would be, first to raise a thermometer to a 

 height something exceeding the natural heat of the human 

 body, and then to ol>ierve at what rate the quicksilver con- 

 tracted upon exposure to the air. F^or this purpose I used a 

 thermometer with a very small biilb, which might show the 

 alteration of heat in a short time. This I held to the fire till it 

 rose to about 120°, and then carried it in a warm glove into the 

 open air. I had with me an assistant with a watch in his hand : 

 and as soon as the mercury had descended to 100°, he began to 

 count the seconds, while 1 continued to observe the thermome- 

 ter, marking the degree of heat at the end of every ten seconds 

 during half a minute. The result rather exceeded my own ex- 

 pectations ; and (being, as far as I know, the only experiments 

 of the kind,) 1 have thought the Society might not dislike to be 

 made acquainted with them. 



