324 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



those slender Aerial Bodies separated and stretcht out (at 

 least, as far as the Neighbouring ones will permit) which 

 otherwise, by reason of their flexibleness and weight, would 

 flag or curl ; but also makes them hit against, and knock 

 away each other, and consequently require more room, 

 then that which if they were compress'd, they would take up, 

 " By these two differing ways, . . . , may the Spring of the Air 

 be explicated. But though the former of them be that, which 

 by reason of its seeming somewhat more easie, I shall for 

 the most part make use of in the following Discourse : yet 

 am I not willing to declare peremptorily for either of them, 

 against the other (" New Experiments touching the Spring 

 of the Air," 1660, pp. 22-26;compare Works, 1725, II. 410). 



The second explanation, which Boyle borrowed from 

 Descartes, resembled somewhat closely that which is gener- 

 ally adopted at the present day under the name of the 

 KINETIC THEORY OF GASES. According to this theory, gases 

 consist of elastic particles, moving with a high velocity, and 

 by their incessant collisions producing a constant pressure 

 upon each other and upon the walls of the containing 

 vessel. Their velocity is an expression of the heat energy 

 which the gas possesses, and increases with the temperature 

 in such a way that the temperature of a gas may be 

 measured by the pressure which it produces in a vessel of 

 given volume. 



Boyle (1662) measures the condensation and rarefaction 

 of the air, Boyle's law. 



In a " Defence of the Doctrine touching the Spring and 

 Weight of the Air .... against the Objections of Francis- 

 cus Linus," published in 1662, Boyle described "two new 

 Experiments touching the measure of the Force of the 

 Spring of Air compressed and dilated" (Defence, pp. 57 68; 

 Works, 1725, II. 670). 



In the first experiment, air was compressed by means of 

 a column of mercury into one limb of a long glass tube, 

 shaped like an inverted syphon (Fig. 46). The column of 



