COMPUTATION OF SQUARES AND CUBES. 123 



Fig. 2 reprefents a iimple rale and firing for drawing ovals Inftrument for 

 «u paper. A C B is a filken thread, fixed at A, and capable ^'^^wing ovals, 

 of being letigthened, fhortened, and fixed b)' a fcrew B at the 

 other end. This fcrew B can be placed, by a longitudinal 

 groove in the ruler, at any Hi fiance from A, and can be made 

 to pinch the thread upon any one of the divifions of the rule. 

 At C is a pencil to be moved in the bend of the thread. It 

 mad be held upright, and it would be eafy to contrive means 

 of keeping it fo ; but it does not feem an object of fufficient 

 neceffity to add to the price of the inflrument. 



In the ufe, (et A at one focus of the intended oval and B 

 at the other. Allow the firing to extend till the pencil marks 

 the extremity of the conjugate diameter. Draw the femi-oval 

 by moving the pencil along in the flretched thread: Then 

 reverfe the points A and B, placing them refpe^ively on the 

 foci occupied before by each other. Draw the other femi- 

 oval, which completes the figure. 

 I am. Sir, 



Your obliged correfpondent, 



R. B. 



XIV. 



On tite Computation of Tables of Squares and Cubes. In a Letter 

 from H. G. 



To jyrr. NICHOLSON. 

 SIR, Sept. 8, 1804-. 



l\S I can employ my time in a more ufeful, pleafant, and Introiuftioa.' 

 advantageous way than by making tables of any kind, I have 

 no defire on ray own account to trouble your readers with the 

 following remarks, and fhall therefore leave it entirely to your 

 choice to notice them or not in your Journal. 

 I am. Sir, 



Yooj humble fervant, 



H. G. 



YOUR correfpondent E. O. in his note, p. 79 of your On die compa- 



Journal for this month, has very properly pointed out an error '^''°" °^ "'''*=• 



''*''* .of fquarcs and 



«n cubes. 



