relative to Black, Watt, and Cavendish. 495 



for diving might be tried by the persons bespoke by Mr. Pepys 

 for diving, it was ordered that this diver should be sent to Mr. 

 Hook to be instructed by him touching the use of the said 

 boxes under water." 



" On the 29th of March an experiment was made for the 

 generating of air by putting aquafortis and the powder of 

 oyster-shells in a small glass phial under water, and whelming 

 a large glass filled with water over it to receive the steam to 

 be generated by the corrosion : the success whereof was that 

 the whelmed glass was filled about ith full with an aerial sub- 

 stance — ordered to be set by till the next meeting." 



" It was moved that a way might be thought on, of pro- 

 ducing an air that might be useful to respire." 



" On the 12th of April Mr. Boyle proposed [inter alia] to 

 try whether the eggs of silkworms and snails would be hatched, 

 as also whether seeds would germinate and thrive, all, in an 

 exhausted receiver." 



" Dr. Goddard affirmed that plants live as much upon air 

 as the earth." 



" Mr. Hook, being called upon to give an account of one 

 of the last days experiments touching the air generated by 

 aquafortis and the powder of oyster-shells, reported that the 

 greatest part of it was returned into liquor." 



" The same was ordered to make, the next day, the expe- 

 riment of generating air with bottled ale, supposed to be 

 wholesome to breathe in, which the air hitherto generated is 

 not*." 



On June the 14-th " an account was given of an experiment 

 of the growth of water-cresses in a receiver." Having been 

 kept for a week in an exhausted receiver they showed no 

 growth ; the air being admitted " they grew in the same time 

 two or three inches." 



These experiments remained unprinted : but a more com- 

 plete discussion of the same subjects not long afterwards ap- 

 peared. In 1668, at the early age of 23, Mayow, adopting 

 the theory of Hook, published a tract in which " he delivered 

 his thoughts of the use of respiration, waving those opinions 

 that would have it serve either to cool the heart, or to make 

 the blood pass through the lungs out of the right ventricle of 

 the heart into the left, or to reduce the thicker venal blood 

 into thinner and finer parts, and affirming that there is some- 

 thing in the air absolutely necessary to life, which is conveyed 



* On the 24th of May in this year (1764) the following record is entered : 

 "The king had been pleased himself to make the observation (on the 

 variation of the needle) at Whitehall, and had found no variation at all, 

 the needle standing in the meridian." 



