REPETITION OF CAVENDISH EXPERIMENT. 107 



earth was five and a half times that of water. The ex- 1839. 

 periment of Cavendish was published in 1798. It is much 

 to be wished that it should be repeated on a larger scale, 

 but the expense of the apparatus will probably deter in- 

 dividuals from the attempt.' 



In a pencil note in the margin of the same page I 

 find- 



c This was, I believe, the remote cause of the repetition First sug. 

 of the experiment. Being, a few months afterwards, in 

 the year 1335, on the Council of the Astronomical Societ} r , 

 something was said about the mean density of the earth, 

 and I happened to say, " I wish Cavendish's experiment 

 could be repeated." Mr. Airy immediately said, "Ah, 

 that would be a good thing." Others agreed, and a 

 committee was appointed on the spot " to consider of the 

 practicability," &c. The result was the repetition of the 

 experiment.' 



The history, the nature of the formulse for the calcu- 

 lations, and the results of the discovery, are all given 

 by Mr. De Morgan in the articles ( Attraction,' ' Caven- 

 dish Experiment,' ' Weight of the Earth,' and others, 

 in the Penny Cyclopcedia, and in a sufficiently popular 

 form in an article in the Companion to the Almanac for 

 1838. 



Mr. Baily's repetition, commenced in 1838, was carried 

 on in a small upper room twelve feet by twelve, as 

 far removed as possible from the noise and shaking of 

 street traffic. It was, of course, an object of interest to 

 all scientific friends, and Mr. Baily's genial kindness in 

 explaining his beautiful apparatus and showing his pro- 

 gress was one of the pleasant accompaniments of his 

 important work. The apparatus designed and con- 

 structed by Mitchell, who did not live to use it, had 

 been used by Cavendish, and afterwards by Mr. Baily, 

 but so greatly improved and added to by the last ex- 

 perimenter that it could hardly be called the same. I saw 



