I 







IW 



rk 



>-■ 



288 



KKrouT — 1884. 



Proposed Small Screw Gaufie, 



G. It is evident that by taking the exact snecessive ])Owers of 0-0 for 

 the pitch, complex mimbers would soon bo arrived at. Such diraen,sioiis 

 would, however, involve a degree of accuracy wliich is hardly attain- 

 able in practice, and it may bo shown that, with two significant figures 

 employed throughout to express the pitch, the degree of accuracy likely to 

 be attained in screws of the kind under consideration is reached. Relyin? 

 on this fact, the series of pitches given in Column VI.' is arrived at fin' 

 screws ranging from •230-inch to the smallest in use, 0'01-inch in diameter, 

 in place of the mathematically exact series obtained by raising O'!' to 

 successively higher powers.'' And this is the series which the Committee 

 recomnionds for adoption. 



7. Viewing the numbers thus obtained in the first place merely a.'^n 

 graduated series of pitches, and ignoring the unit of measurement, it 

 may be admitted that the series of powers of O'l* from which they are 

 deduced is perhaps as good a one as can be suggested for the purpose, and 

 it is found to very closely correspond with experience. Thus Column VI., 

 which gives the nearest approximation to this series that is practically 

 required, is well adapted for such a system of screws. It is to be ob.servd 

 that in selecting a series of pitches there are three simple alteriiativos 



• It may bo incidentally pointed out hero that thi.s series oomprisos two .scri'v.-, 

 with pitclu's of 1 nun, and 025 nun., whicli would bo serviceable lor niicroiiictcr." 



• .Sir Joseph Whit worth's gauge, in general use, ends at ^-in., where this coiiiintncc' 



