Fuller's Calculating Slide-Rule. 61 



(2.) Division with a Constant Divisor. 



-=- = x, — = x, -^ = of, &c., may be resolved into 

 OOO 



(?M 



a?' as" 



i.e. (log. (7 — log. i) == log. cZ — log. x = log. cZ' — log. x' = &c. 



This resolves the operations into questions of proportion. 

 If, therefore, in the first example, the indices be so arranged 

 that 1 on the scale is opposite the movable index, and C 



opposite the fixed index, the ratio-^, will be represented, 



logarithmetically, by the distance between the two indices ; 



and as this ratio is the same for all the other ratios, viz., 



— , -^7 , — , &c., it will be only necessary to bring the 



various values, d, d', d" , &c., to the movable index, and the 

 results, viz., as, x, x* ', &c, may be read off, in turn, at the 

 fixed index. In like manner, in the second example, the 

 fixed index is set at 1, and the movoMe index at C; and 

 then the scale is moved so as to bring the different values — 

 d, d\ d/ } &c. — to the movable index, when the answers — 

 x, x', x'\ &c. — will be found at the fixed index.* 



Art. X. — Note on the Habits of Hermit Crabs. 

 By A. H. S. Lucas, M.A., B.Sc. 



[Read 12th November. 1885.] 



A statement is constantly repeated in the text-books of 

 zoology that the hermit crabs always protect their soft 

 abdomens by taking up their abode in the empty shells of 

 gasteropods. Thus Nicholson says : " The animal is com- 

 pelled to protect the defenceless part of the body in some 



* It is stated (in a footnote) in the Instructions issued with the -Rule that 

 the two stops, which were fixed to the instruments first made, so that the 

 beginning of the scale (100) might be brought at once to the fixed index, are 

 now omitted as useless ; but this is to be regretted, as, from the second set of 

 examples shown above, it will be seen that such stops will prove of great 

 advantage. 



