78 THEORY OF LIGHT AND COLOUR-. 



guiar piece of brafs (thus \) to fupport the pendulum. This 

 lupport is made fan with fcrews to the rifiwr-board at the bot- 

 tom, and to the frame-plate of the clock at the top. Who in- 

 vented this fupport I know not, but it appears a very excellent 

 method of giving liability to the point of fulpeniion of the 

 pendulum . 

 Refult. I "his clock has now been going near feven years. It vibrates 



1 ° -19' on each fide of the perpendicular, from which I have 

 not feen it vary more than 2', except once in a very hard froir, 

 and as it feldom varies fo much as 2' in its femi-arc, this caufe 

 of error in the pendulum feemsto be very nearly removed. It 

 has been cleaned only once fince it came into my pofleffion, 

 but this made no alteration, either in its arc of vibration or its 

 rate of going. 



I am, with much refpect, 

 Sir, 



Your very humble fervant, 



EZEKIEL WALKER. 



Importance of 

 general princi- 

 ples in fcience. 



Obje& of the 

 prefent diflerta 

 tion. 



VII. 



On the Theory of Light and Colours*. By Thomas Young, 

 M. D. F.R. $. Projefor of Natural Pkilofophj in the Royal 

 I nfiitution, 



ALTHOUGH the invention of plaufible hypothefes, inde- 

 pendent of any connection with experimental obfervations, 

 can be of very little ufe in the promotion of natural know- 

 ledge ; yet the difcovery of fimple and uniform principles, by 

 which a great number of apparently heterogeneous phenome- 

 na are reduced to coherent and univerfal laws, mutt ever be 

 allowed to be of considerable importance towards the im- 

 provement of the human intelLect. 



The object of the prefent cHifertation is not fo much to pro- 

 pofe any opinions which are abfolutely new, as to refer fome 

 theories, which have been already advanced, to their original 

 inventors, to fupport them by additional evidence, and to ap- 

 ply them to a great number of diverfified facts, which have 

 hitherto been buried in obfeurity. Nor is it abfolutely ne- 



* Iii fupport of the truth of that hypothefis, which afcrihes the 

 phenomena to unduiatoiy motions cf an extremely eiaftic and. rare 

 fluid. From the Philof. Trajif. 1802.— N. 



ceUary 



