236: ' Qiiesiion by John Harnett, Esq. 



curved lines, and have also seen its mode of operation, and 

 have uispected a great variety of curves which have been de- 

 scribed by means of it. We have no hesitation in saying, that 

 we regard this apparatus as most simple and ingenious, capa- 

 ble of producing, with the utmost facility, an indefinite variety 

 of curves, comprehending those which have been the subject 

 of mathematical research, and numerous others, which cannot 

 fail to be of great utility in naval architecture, in the ornamen- 

 tal departments of civil architecture, and in the formation of" 

 patterns in the imaginative regions of the arts. To mathema- 

 ticians, the use of this apparatus will suggest a variety of in- 

 quiries in reference to new and curious curves, whose proper- 

 ties have not as yet been investigated; while to architects, 

 shipwrights, engravers, and many others, it will be found sub- 

 servient to the most fertile and interesting applications." 



(Signed,) Oltnthus Gregory, LL.D. Professor of Ma- 

 thematics in the Royal Military Academy. 

 S, FI. Christie, M.A. of the Royal Military Academy. 

 Arthur AiKiN, Secretary to the Society of Arts, &c. 

 Thomas Tredgold, Civil Engineer. 



The Apparatus may be had at Mr. Taylor's Architectural 

 Library, Holborn ; at Mr. T. Jones's, Philosophical Instru- 

 ment-maker, Charing Cross; and at Mr. Jopling's, 24; Somer- 

 set-street, Portman-square. 



A friend who has seen the machine assures us that nothing 

 can be more simple, more easily managed, or more fi'ee from 

 any thing, to obstruct tlie opex'ator from seeing the describing 

 point. To engravers it seems likely to be an invaluable acqui- 

 sition. It describes all species of the conchoidal, elliptic, car- 

 dioidal, and many other species of curves ; every section of a 

 ship, so that they shall range; arches bf every form that can be 

 desired : and it may be successfully applied to describe an im- 

 mense variety of patterns, which you can make perfectly symme- 

 trical, identical, or vary in any manner. 



An account of the principles on which the apparatus is con- 

 structed, is given by the inventor in a small work (sold by 

 Taylor, Holborn,) entitled " The Septenary System of Gene- 

 rating Curves by continued Motion," 



OUESTIOU BY JOHN HAMETT, ESQ. 



"In the construction of Pythagoras's theorem, lines are drawn 

 from the acute angles of the right, angled triangle to the op- 

 posite angles of the squares described upon the sides contain- 

 ing the right angle ; and a line is drawn from the right angle 

 parallel to either side of the square described upon the side 

 -Htending the right angle. Now, as it so happens that these 



three 



