Noiices rcsjjccihig Ncto Booh. -219 



■tage will, when understood, occasion this kind of teetli lo he 

 almost universally adopted. 



An easy mode of computing the real 7-adius of a '.\'heel or 

 pinion, of this construction, is given : hut we could have heen 

 better pleased, if the manner of findiiig the real radius, by 

 geometrical construction, had also been explaiued, the advan- 

 tages of which mode, in similar cases, the Editor appears to 

 be fully aware of, and therefore we have been surprised that 

 he should liere have neglected it. He remarks, that an in- 

 genious rule employed by Mr. Murray, of Leeds, for finding the 

 length of teeth, is founded on the projjeilies of involute teeth, 

 and therefore a})plicable, to such teeth only. The autlior had 

 given an erroneous method of forming the teeth of pinions for 

 rack-work, which his Editor has detected, and supplied a rule 

 for finding the real radius of the pinion, and also described 

 tlie form of the teetli for a rack to move a pinion. 



The subject of beveled wheels, has tilways been esteemed 

 an intricate one ; because it has been so treated, as to involve 

 the consideration -and description of curves of double curva- 

 ture ; but r.Ir. Tredgold has been fortunate in discovering a 

 new principle of forming these teeth, which is simple, and very 

 easy of aj^plication ; and in consequence of the very general 

 use of beveled wheels, in modern macliines, and the im- 

 mense advantage of well-formed teeth for such, this discovery 

 will prove a valuable one. The most important of the pro- 

 perties of involute teetli are pointed out, wliich show, that they 

 can only be useful in particular cases. In addition to some 

 supplementary definitions of the author, liis Editor has now 

 subjoined some interesting definitions cf j)orver, force, momen- 

 tum and raechnnical poiver. It is well known that the nature 

 o(Jhrce, was a subject of much discussion about fifty years ago, 

 which has been at intervals revived, up to the i)resent time: 

 the importance of settled and clear ideas on the subject, is of 

 the first importance, in all mechanical intjuiries, and in our 

 opinion, the Editor's views are founded in truth. 



The horse's power, was by Mr. Buchanan, made the mea- 

 sure of sLriiin, in the parts of machines, and hence his Editor 

 has taken occasion to imlbld his «wn ideas, on the maximum 

 of effect of animal force; and after an interesting iiupiir}' re- 

 specting the velocity winch corresponds to the maxiuuun efl'ect, 

 lie justly givci the ])rcference loSmeaton's m.easure, of theforce 

 c»f men, as given from the jiapers of that able engineer, by 

 Mr. Farey juuior, tlie writer of the excellent article Watkh 

 ill Dr. Rces's ("yciopa'dia. On ihe strength of the teeth of 

 wheels, (he ICditor enters into some new investigations, fWim 

 whence he derives si»)ple ai>d general rules, for guiding fhe 

 E c 'J praciical 



