396 PHILOSOPHICAL TRANSACTIONS. [aNNO l66g, 



inconsiderable remarks touching the nature and virtues of all the drugs which 

 compose it. * 



A Description of Dr. ^afterwards Sir J Christ. Wren's Engine for 



Grinding Hyperbolical Optic Glasses. Translated from the Latin. 



iV» 53, p. 1059. 



Let there be three bodies, P, Q, R, (pi. 9, fig. 7,) fit for grinding; of which 

 let P and Q be equal, and of the shape of a pillar, and R resemble a lens. Let 

 P have a rotation about the axis AB, Q about CD, and R about EG. Let AB 

 and CD be in different planes, but so posited that EG, being produced, may- 

 be at right angles both to AB and CD. Lastly, let the bodies approach to each 

 other, as much as necessary ; still however preserving the same situation and 

 position of their axes. 



I say, that by the rotation and mutual attrition of these bodies, new geometric 

 cal figures will arise, of which P and Q will be equal hyperbolical cylindroids, 

 and R an hyperbolical conoid, given both in species and magnitude. 



I have both the demonstration, and the model of the machine itself for 

 grinding hyperbolical glasses. To give a figure of it, and to describe it minutely, 

 would cause more trouble, both to the artist and myself, than the inventing of 

 it. For since the geometrical principles are already explained, it will be easy to 

 guess what sort of an instrument it is. The parts are three oblong, plain, 

 strong, and smooth boards, laid upon each other. The lowest and middlemost 

 sustain the unequal supporters (or handles supporting the mandril) placed alter- 

 nately ; which is necessary, on account of the obliquity and decussation of the 

 two mandrils. The poppet-heads or supporters, disposed according to the 

 length of the uppermost board, are equal to it ; and the mandril is inserted into- 

 a perforation in the nearest poppet-head. I omit the several wheels, rollers, 

 strings, weights, screws, and the other apparatus necessary for strengthening the 

 machine, and givhig it a swift motion. P belongs to the lowest board ; Q to the 

 middlemost ; R to the uppermost; R is a lens of glass; Q a grinding tool that 

 grinds the lens ; P the director correcting the grinding tool ; which, moving 

 obliquely, and in a direction different from that of the lens and grinding tool, 

 continually efi'aces and grinds off^ any defect communicated to the model by the 

 attrition of the lens, and its own matter. 



Wherefore, since the formation of the hyperbolical conoid is so simple and 

 easy, being produced by only circular motions ; and since the motion is double 



• In modern pharmacy preparations less compound have been introduced in place of these heteroi- 

 geneous farragoes. 



