8 THE VOYAGE OF H.M.S. CHALLENGER. 



(in 17G4) the curiously important additional fact that it diminishes when the tempera- 

 ture is raised. As his papers, or at all events the second of them, seem to have fallen 

 entirely out of notice, 1 and as they are exceedingly brief and clear, I think it well to 

 reproduce some passages textually from the Philosoi^iical Transactions of the dates 

 given above. 



" Having procured a small glass tube of about two feet in length, with a ball at one 

 end of it of an inch and a quarter in diameter ; I filled the ball and part of the tube 

 with mercury ; and, keeping it, with a Fahrenheit's thermometer, in w r ater which was 

 frequently stirred, it was brought exactly to the heat of 50 degrees; and the place where 

 the mercury stood in the tube, which was about 6^ inches above the ball, was carefully 

 marked. I then raised the mercury, by heat, to the top of the tube, and sealed the 

 tube hermetically ; and when the mercury was brought to the same degree of heat as 

 before, it stood in the tube ~ of an inch higher than the mark. 



" The same ball, and part of the tube being filled with water exhausted of air, instead 

 of the mercury, and the place w T here the water stood in the tube when it came to rest 

 in the heat of 50 degrees, being marked, which was about 6 inches above the ball ; the 

 water was then raised by heat till it filled the tube ; which being sealed again, and the 

 water brought to the heat of 50 degrees as before, it stood in the tube ~ of an inch 

 above the mark. 



" Now the weight of the atmosphere (or about 73 pounds avoirdupois) pressing on 

 the outside of the ball and not on the inside, will squeeze it into less compass. 2 And by 

 this compression of the ball, the mercury and the water will be equally raised in the tube ; 

 but the water is found, by the experiments above related, to rise ^ of an inch more 

 than the mercury ; and therefore the water must expand, so much, more than the 

 mercury, by removing the weight of the atmosphere. 



" In order to determine how much water is compressed by this, or a greater weight, 

 I took a glass ball of about an inch and £ in diameter which w-as joined to a cylindrical 

 tube of 4 inches and ^ in length, and in diameter about ± of an inch ; and by weighing 

 the quantity of mercury that exactly filled the ball, and also the quantity that filled 

 the whole length of the tube; I found that the mercury in ~ of an inch of the tube 

 was the 100,000 part of that contained in the ball ; and with the edge of a file, I 

 divided the tube accordingly. 



" This being done, I filled the ball and part of the tube with water exhausted of air ; 

 and left the tube open, that the ball, whether in rarefied or condensed air, might always 

 be equally pressed within and without, and therefore not altered in its dimensions. 



1 Perhaps the reason may be, in part, that by a printer's error the title of Canton's first paper is given (in the 

 Index to vol. lii. of the Phil. Trans.) as " Experiments to prove that Water is not compressible." 



3 " See an account of experiments made with glass balls by Mr. Hooke (afterwards Dr. Hooke) in Dr. Birch's 

 History of the Royal Society, vol. i. p. 127." 



