316 A. B. '(^uinhy on the Spiral of Archimedes. 



On the subject of the injury which each engine is capable 

 of producing, in case an explosion takes place, the committee 

 are amply prepared to decide. • 



Respectfully, 



' A. B. QUINBY. 



New- York, June 28, 1824, 



Art XV. — 0?i the Spiral of Archimedes ; by A. B. QuiNBYt 



Prof. Silliman, 



Dear Sir, 



The subject of describing the spiral of Archimedes, by 

 means of an instrument, was proposed at a meeting of the 

 Mathematical Club in June 1822. A few days after the 

 problem was given, I invented the instrument which the 

 drawing you will receive with this letter represents. 



At the time the subject was suggested, the Club were not 

 aware that an instrument for describing this curve had been 

 invented by Ciairaut. After my discovery, I learned from 

 my scientific friend. Dr. Adrain, that the Memoirs of the 

 Academy of Sciences contains an account of an instrument 

 invented by Ciairaut, which describes many curves, and 

 fimong them the spiral of Archimedes. 



Reference to the Plate. 



The upper drawing, Fig. 1, Plate V. represents a horizon- 

 tal view of. the instrument, standing on a table. The lower 

 drawing represents a vertical view of the instrument, in the 

 same position. The part cc' is a cylinder, about which the 

 thread th is wound. This cylinder is held permanent by the 

 scew Sw, which passes through its centre. The braces bb' 

 (of which there are four) enter, by small shoulders, into the 

 bars AL and DG, and support, at their upper extremity, the 

 inner ring rr'. This ring, and the braces and cylinder, al- 

 ways remain at rest. The outer ring RR', which carries the 

 bars BB', rests upon a shoulder of the inner one rr', and 

 may be made to revolve to the right, or the left, at pleasure. 

 A section of these two rings is seen at the point v. The part 



