Observations on a New Scale for the Thermometer, 417 



per place for O would undoubtedly be that point at which 

 heat commences ; but the physical causes, which are known 

 to exist, to prevent that point being ever ascertained, ex^ 

 elude entirely the hope ot" fixing it there ji, to say nothing 

 of the inconvenience which must arise trOm the scale be- 

 ing incumbered with a multiplicity of figures, at that part 

 which is most familiar and in most frequent use. 



Hence we are under the necessity here, as in many other 

 instances, of uj;ing the positive and negative signs. 



Having been for a v^ery long time engaged in thermome- 

 trical experiments and observations, — the imperfection of 

 all the scales in use, and the consequent dissatisfaction of 

 V/ario»us persons respecting them, frequently occurred to me; 

 and it is long since that I was impressed with the opinion, 

 strengthened by ihat of several of my friends, of the pre- 

 ference which was due to the one I am now about to men- 

 tion. 



It has been ascertained by physiologists as a fact, and 

 of which I have perfectly satisfied myself, by repeated ex- 

 periments on others as well as myself, that 62 of Fahren* 

 heit is that point at which the human body in a state of 

 health is unconscious of either heat or cold, that is, in a 

 state of rest, or when free from any considerable bodily 

 exertion ; and this is really the case at all seasons of the 

 year, in this climate, and probably in all other climates; for 

 the temperature of the human body, or blood heat, as it is 

 called, is determined every where to be 98, and it has been 

 found that the vital functions have the power of regulating 

 the sensation of heat; so that any temperature above 62 

 of Fahrenheit, under ordinary circumstances, shall give a 

 sensation of /leat, and any temperature below 62 of Fahren- 

 heit a sensation of cold*. 



* Dr. Cullen, in speaking- of the influence of temperaUtre on the human 

 body in this climate, says : *' If the temperature at any time applied is undef 

 62 degrees, every increase of temperature applied will give a sensation ot* 

 heat ; but if the increase of temperature docs not arise to 62 degrees, the 

 sensation produced will not continue long, but be soon changed to a sen- 

 sation of cold. In like manner, any temperature applied to the human 

 body lower than that of the body itself, gives a sensation of cold ; but if 

 the temperature applied doe» not go below 62 degrees, the sensation of 

 cold will not continue long, but be soon clianged to a sensation of heat." 

 CuUen's Practice of t>hysic, vol. i. 1 784, p. 9 1 , 92. 



This point is so nicdLy balanced, and so accurately jU^t,Tiz- at 9€ degree* 

 below blood-heat, or 98, that a variation of one, or at most two degreesj 

 above or below that point, actually produces a sensation of heat or cold ; and 

 which, by experiment pTQpcxly made, would be found to be equally the case 

 in the lorrid and frigid zone as in temperate climates : hence this point may 

 be considered as the actual, or natural nought^ with respect to heat and cold 

 on the thermometer. 



Voi. 35, No. 146. June 1810. Dd Upon 



