320 Notices respecting New Books^ 



with regard to the pitches and breadths of the teeth of 

 wheels. 1 do not pretend to more than a mere approxima- 

 tion towards general rules; vet, were this judiciously done, 

 T am of opinion that it might be useful to the millwright 

 who has not had leisure or opportunity for scientific in- 

 quiries. A rule, though not absolutely perfect, is better in 

 all cases, than to have no guide whatever." 



In order to clear the ground of inquiry, he proceeds to 

 make some general ol'.^ervations on the ic/iecl-ivork oj mills, 

 which we think merit attention. The elementary propo- 

 silions which serve to guide the inquiry are next laid down, 

 and their application considered. Afterwards the measure 

 of the stress on the teeth of wheels is considered. 



" In order to take experience as our guide, several ex- 

 amples in the annexed tables, actually in use, areselccied. 



" The pilch, velocity, a^id strain, are all stated ; the 

 stirain is measured by the horse's power ; at which the resist- 

 ance is valued. Horse's power is a term now in general use, 

 to express the force required in order to drive any kind of 

 mill, and it may be proper here to give some further ac- 

 count of it. 



*' Horse's power. Although horses are not all of one 

 strength, vet there is a certain force now generally agreed 

 upon among those who construct steam engines, which 

 force is denominated a horse's power, and hence steam en- 

 gines arc distinguislied, in size, by the number of horseg' 

 power to which they ar; said to be equal." 



The table contains a number of examples of wheel-work 

 in actual use driven by water wheels, horse mills and steam 

 engines. On this table a number of observations are made 

 and [)ractical pules deduced. These are followed by a very 

 useful communication from Mr. John Roberton, engineer. 



The next subject we consider as also very important, and 

 on which we believe nothing had previously appeared in 

 print. It is entitled " Practical Olservalions uith regard to 

 the making of Pai terns of Cast Iron IVhocls." 



The book concludes with Mr. Donkin's table of the radii 

 of wheels, which mav ^ave millwright'? llic trouble of 

 much calculation, 



UpoD 



