PHYSICS OF THE EIGHTEENTH CENTURY. 285 



Royal Society presented Dollond with the Copley gold medal, and his 

 fame became European. In 1761 he was elected a Fellow of the Royal 

 Society, but he did not live long to enjoy his honours. On the 30th of 

 November, in the same year, while reading a mathematical treatise, he 

 was seized with apoplexy, and died in a few hours. His son, who had 

 been associated with him in the optical business, successfully carried 

 on the establishment for many years. 



With the eighteenth century we enter upon a branch of physical 

 science which took form only within that period. Its phenomena un- 

 ceasingly present themselves, and there is no department of natural 

 science with which they are not more or less connected. Its laws 

 affect our every-day life and govern our industrial arts in a boundless 

 measure. It may be asked how it has come to pass that a science 

 concerned with phenomena so important and so constantly under ob- 

 servation has been so late in its origin. It was not for the want of facts. 

 But facts by themselves, however numerous and however important, 

 do not constitute a science. A science is constituted only when the 

 facts are co-ordinated by laws, and these laws in their highest generality 

 always formulate quanthj/ve relations between phenomena. Before any 

 such relations can be formulated, reliable measures of the phenomena 

 must be obtained, and it has been noticed that the development of 

 every branch of science has always kept pace with the means of ob- 

 taining exactness in the measurements of its fundamental phenomena. 

 The science we now enter upon had waited for ages for its instrument of 

 measure a very simple, and now a very familiar one. An ordinary 

 form of it is represented in the annexed cut, Fig. 136. The 

 reader will at once recognize the Thermometer, and perceive 

 that the remarks just made apply to the science of Heat. But 

 already we have referred to the thermometer as having been 

 in existence in the preceding century (p. 106). The appa- 

 ratus, indeed, bore this name, but it was in reality no mea- 

 surer of heat, or even of temperature; for although it would 

 indicate changes of temperature, there existed no standard 

 with which the observation could be compared. The inven- 

 tion of the instrument in this imperfect form has been attri- 

 buted to the various individuals whose names have been 

 already mentioned in connection with it, and also to others. 

 The invention of the thermometer as a truly scientific instru- 

 ment may be more properly referred to the individual who 

 first supplied the means of making its observation compar- 

 able. This appears to have been no other than the illustrious 

 Newton, who describes in the " Philosophical Transactions " 

 of 1701, a thermometer with fixed points of temperature. FIG. 136 

 Linseed-oil was the expansible liquid employed in this ther- 

 mometer, and the lowest fixed point of the scale was obtained by 

 plunging the instrument in snow, and marking the point at which the 



