TOL. IX.] PHILOSOPHICAL TRANSACTIONS. 175 



To all which he annexes occasionally something that relates to the priority of 

 the invention of the circular pendulum ; and likewise a description of a wheel- 

 work, which, he says, may be called the perfection of such work, having the 

 perfectest idea, he thinks, that toothed wheel-work is capable of performing the 

 same effect, as if the wheel and pinion had an indefinite number of teeth. 

 Which done, he describes the frame for keeping the instrument, which is the 

 main argument of this book, in its perpendicularity, and yet always in the azi- 

 muth of the celestial object ; with a digression of the great use of this principle 

 in dialing, equaling time, clock-work, &c. 



He mentions also a mechanical way he has, of calculating and performing 

 arithmetical operations, much quicker and more certainly, than can be done by 

 the help of logarithms. 



He concludes the whole by showing many of the particular uses of this new 

 quadrant, as — 1. For measuring the refraction of the air. 2. For regulating the 

 places of the fixed stars and of the planets. 3. For stating the latitude of places. 

 4. For examining the influences of the planets on the earth. 5. For measuring 

 the quantity of a degree upon the earth. 6. For measuring seen distances. 

 7. For levelling. 8. For taking the diameters of the sun, moon, and other 

 planets. Where, by the by, are mentioned two other instruments, one for 

 taking diameters to seconds; the other for looking on the body of the sun 

 without injury to the eyes. 



^ Letter of the Learned Franc. Linus, to a Friend in London, animadverting upon 

 Mr. Isaac Newton^ s Theory of Light and 'Colours. N° 110, p. 217. 



Honoured Sir. — Understanding that things of the nature I now write are 

 always welcome to you, from what hand soever they come, I thought good to 

 mention, that perusing lately the Phil. Trans, to see what I could find therein, 

 in order to a little treatise of optics I have in hand ; I lighted, in p. 3075, upon a 

 letter of Mr. Isaac Newton, wherein he speaks of an experiment he tried, by 

 letting the sun beams through a little hole into a dark chamber; which 

 passing through a glass prism to the opposite wall, exhibited there a spectrum 

 of divers colours, but in a form much more long than broad; whereas according 

 to the received laws of refraction, it should rather have appeared in a circular 

 form. Whereupon conceiving a defect in those usual laws of refraction, he 

 frames his new theory of light, giving to several rays several refrangibilities, 

 without respect to their angles of incidence, &c. 



Truly Sir, I doubt not of what this learned author here affirms ; and have 

 myself sometimes in like circumstances observed a similar difference between the 



