20 REPORT — 1902. 



but very remissly, so that till it be determined whether cold be a positive 

 quality or but a privative it will be needless to contend what particular 

 body ought to be esteemed the jmmum frigidum.' The whole elaborate 

 investigation cost Boyle immense labour, and he confesses that he ' never 

 handled any part of natural philosophy that was so troublesome and full 

 of hardships.' He looked upon his results but as a ' beginning ' in this 

 field of inquiry, and for all the trouble and patience expended he consoled 

 himself with the thought of ' men being oftentimes obliged to suffer as 

 much wet and cold and dive as deep to fetch up sponges as to fetch up 

 pearls.' After the masterly essay of Boyle, the attention of investigators 

 was chiefly directed to improving thermometrical instruments. The old 

 air thermometer of Galileo being inconvenient to use, the introduction 

 of fluid thermometers greatly aided the inquiry into the action of heat and 

 cold. For a time great difficulty was encountered in selecting proper 

 fixed points on the scales of such instruments, and this stimulated men 

 like Huygens, Newton, Hooke, and Amontons to suggest remedies and to 

 conduct experiments. By the beginning of the eighteenth century the 

 freezing-point and the boiling-point of water were agreed upon as fixed 

 points, and the only apparent difficulties to be overcome were the selection 

 of the fluid, accurate calibration of the capillary tube of the thermometer, 

 and a general understanding as to scale divisions. It must be confessed 

 that great confusion and inaccuracy in temperature observations arose 

 from the variety and crudeness of the instruments. This led Amontons 

 in 1702-3 to contribute two papers to the French Academy which reveal 

 great originalit}' in the handling of the subject, and which, strange to say, 

 are not generally known. The first discourse deals with some new 

 properties of the air and the means of accurately ascertaining the 

 temperature in any climate. He regarded heat as due to a movement of 

 the particles of bodies, though he did not in any way specify the nature 

 of the motion involved ; and as the general cause of all terrestrial motion, 

 so that in its absence the earth would be without movement in its 

 smallest parts. The new facts he records are observations on the spring 

 or pressure of air brought about by the action of heat. He shows that 

 different masses of air measured at the same initial spring or pressure, 

 when heated to the boiling-point of water, acquire equal increments of 

 spring or pressure, provided the volume of the gas be kept at its initial 

 value. Further, he proves that if the pressure of the gas before heating 

 be doubled or tripled, then the additional spring or pressure resulting 

 from heating to the boiling-point of water is equally doubled or tripled. 

 In other words, the ratio of the total spring of air at two definite 

 and steady temperatures and at constant volume is a constant, inde- 

 pendent of the mass or the initial pressure of the air in the thermometer. 

 These results led to the increased perfection of the air thermometer as a 

 standard instrument, Amontons' idea being to express the temperature at 

 any locality in fractions of the degree of heat of boiling water. The great 

 novelty of the instrument is that temperature is defined by the measure- 



