146 



NATURE 



[April 19, 19 17 



most elementary character relating- to propulsion 

 by recoil, and in particular to the action of screw 

 or other propellers when kept fixed relative to 

 the surrounding- medium. It is thus based en- 



when a mathematician speaks of ok, he riieans 

 a multiplied by h. Of course, the amount of 

 information thus obtainable regarding the be- 

 haviour of such a complex mechanism as ah air- 



a o u c . K.- 



o tiUi- S 5 " 

 i c ^- i5 MC 



- a2 -; .-^-C g. 

 " c o "J3 u-s 



2 Ogx ex g 

 Ml 3 S c aj * J. 



jjg O. " u O 



d 2 ■ •- = . 

 -^i ^'fi'c'dc t* 



S -3. " rt 5 - c - < 



CJ< -j'f^ dj^ XP ^ 



1^1- nil 



£ •S'a.' 5 ".y o 



£^ !>= ^ C 3 5 U 



^•2- -s . S o >< 



c.S S- -"S 



. g be,; .^ca a" 



D £ C « U— A 



c*ii S ? E j= ■« 



rt « S • ' ' '" 





^<c5'. 



'r sec" x.Si E* 



■r "^<'-3 p . 2 t S 



o . oj c dj o rt fa. 

 •^ . a <J . = ~ V^c 

 j: ^ ji S dj5 >> c " 



•° CtH .^< Si r>,'C 



.So 13 si ^r? 



" 3 Sc D. 2.- '^ o 



tirely on the principles of momentum and energy, 

 and the formulae given are all immediately intel- 

 ligible to any beginner who has mastered the 

 somewhat illogical notation, according to which, 



NO. 2477, VOL. qql 



screw i.s comparatively small. The author makes 

 his formulae depend, amongst other things, on the 

 mean velocity of the issuingf-jet, its mass per 

 unit time, and the area or diameter of the final 



