218 Notices respecting Ne-js Books. 



equal, it would be still more cliHicult to apply a vernier to tFie 

 scale, though it is In- no means impossible to do so. 

 I am, Gentlemen, 



Your most obedient servivnt, 



Aiigiu=t21, 1S23. IIknry Meiki.e. 



XLVI. Notices respccliiig New Books. 



Practical Essays on Mill-Work and other Machinery; hij Ro- 

 bertson Buchanan, Engineer: the Second Edition, cor- 

 rected, "with Notes and additional Articles, contcdning neio 

 Researches on various mechanical Subjects ; by Thomas 

 TuEDGOLD, Civil Engineer. 2 vols. 8vo. pp. 588, illus- 

 ti'ated by 20 Plates and numerous Wood-cuts. 



'T^PIE ra])id progress of the art o? constructing Machinery lias- 

 -*- rendered works on that subject extremely desirable; they 

 serve at once to i-ecord the progress of the art, and to diffuse 

 and improve it. Amongst other able works, Robertson Bu- 

 chanan's Essays on Mill- Work and Machinery, have contri- 

 buted in no small degree to make known and improve the 

 constructions of the best proficients in this important art. A 

 second edition of this useful work has just made its appearance, 

 edited by Mr. Thomas Tredgold, who has added a consider- 

 able portion of new matter, which to practical mechanicians 

 will be found extremely useful. 



As the Essays diemselves are pretty well known to the 

 public, we shall confine the remarks we intend to make, to 

 the Editor's additions. The first Essay is on the Teetli of 

 "Wheels, wherein is now given, a simple method, by the Editor, 

 of describing Teeth, by arcs of circles, such, as to possess the 

 same advantages, nearlj', as the correct theoretic forms : indeed, 

 he has shown that these forms, have the properties which are 

 ascribed to them by writers, only in the imaginary case, when 

 the acting surfaces have no friction. He gives a general in- 

 vestigation of a rule, for ascertaining the smallest number of 

 teeth there should be on a pinion, to produce uniform motion : 

 the calculations which M. Camus had made on this subject, 

 being confined to particular cases, and these not pracdcal 

 ones. The Editor next shows the advantage of forming the 

 teeth of impelled wheels or )iinions, so as to resemble the 

 staves of trundles, giving to the imjjelling pinions or wheels, 

 teeth of a proper figure, to act u}ion the stave-tbrmed teeth, 

 of the impelled wheels or pinions : by this very simple arrange- 

 ment, the greater part of the action of the teeth, will occu.r, after 

 they have passed the line of centres. This iir.portant advan- 



ta.o-e 



