INVENTION '^"^ CHRONOMETERS, &CC. ^\^^ 



vibration »^a spring might be always supposed of equal dura- 

 tion •* and that advantaee Dr. Hooke asserted himself to have Dr. Hooke's 

 , , . . . . 1 1-1111 1 claim to the 



attained with his invention in watches, which had been shewn jnventiott, 



to several persons, t The principle, however, could not be gene- doubtful, 

 rally trusted, according to Dr. Hooke himself, who, in the 

 Postscript to his Description of Helioscopes (p. 29), declares 

 that he had explained hoxv the vibrations might be so regulated, 

 es to make their durations either all equal, or the greater^ 

 sloxver, or quicker, than the less, and that in any proportion as- 

 signed. We must suspect that these ideas were not properly 

 digested, or regret that their communication by the author, ill 

 his lectures in Gresham College, was not sufficiently explicit 

 to give precise rules for practice, and fix the attention of watch- 

 makers upon the subject. After those hints, the principle Contrivances in 

 seems to have been very little attended to for many years, HienTto make 

 and the isochronism was frequently attempted to be effected all vibrations 

 by means of mechanical contrivances in the escapement. ^ 

 Harrison endeavoured to accomplish that important object 

 by the form of the back of the pallets ; and on the return 



* Dr. Hooke De Potentia Restitiva. — S. Gravesande's Natural 

 Philosophy, by Desaguliers, 1747. v. i. p. 317, &c. 



Dr. Hooke, in the Postscript to his Description of Helioscopes, 

 gives (Tabula Hf.) a short communication of the general ground 

 of his inventions for pocket watches, in the '* Universal and 

 *' real Character" of Bishop Wilkins. This table has been re- 

 published in the quarto series of Nicholson's Journal, but we do 

 not yet possess a translation of it. Dr. Hooke concludes the post- 

 script above mentioned, with a decimate of the centesme of the in- 

 ventions he intended to publish, and subjoias anagrams to some 

 of them. Those which relate to watches, are the two following : 



" 1. A way of regulating all sorts of watches «r timekeepers, so 

 " as to make any way to equalize, if not exceed the pendulum 

 " clocks now used." But there is no addition of any kind to this 

 article. 



" 3. The true theory o^ elasticity or springiness; and a particu- 

 *^ lar explication thereof, in several subjects in which it is to be 

 " found : And the way of computing the velocity of bodies moved 

 " by them, ceiiinosss 1 1 uu." Which anagram, in the " Lec- 

 *' ture De Potentia Restitiva," is thus explauied,-~J7if vis^ sic 

 tensio. 



t De Potentia Restitiva, p. 5, 



of 



