KNOWLEDGE. 



February. 1915. 



The Leading Journal of Science. 



SIXPENCE WEEKLY. 



SUBSCRIPTIONS. 



Great Britain and Ireland. 



Yearly 28s. Half-yearly 14s. 6d. 



Quarterly 7s. 6d. 



Abroad. 



Yearly 30s. 6d. Half-yearly 15s. 6d. 



Quarterly 8s. 



All Students of Science should subscribe to 

 NATURE, seeing that in it are to be found 

 reviews of all important books of Science, 

 and articles, letters, addresses, and papers 

 on all branches of Natural Knowledge, while 

 its advertisement columns call attention to 

 the latest apparatus put upon the market 

 for scientific research and use. 



Office: St. Martin's Street, London, W.C. 



Direct Vision Spectroscope 



LONG. 





Tliis instrument lias a 

 line micrometer screw with 

 divided drumhead and 

 scale, enablin),' one to pass 

 through the spectrum and 

 to obtam wave-length de- 

 terminations with consider- 

 able accuracy. The prism 

 is of high dispersion, and 

 easily resolves the sodium 

 D lines. A pointer is also 

 htted into a positive eye- 

 piece. 



tjle 



Prices 



' Instrument - £9 10 

 I Stand - .£2 2 



DKLIVHI'V rRO\l STOCK. 



O 



o 



ADAIVI HILGER, Ltd., 



75a, CAMDEN ROAD, LONDON, N.W. 



BROWNING'S 



MICRO-CAMERAS. 



' MICROKAM"-Re,.d.) 



A simple yet perfect Instrument 

 for Photographing Objects 

 under the Microscope 



No. 1. — Mahogany 5s. 



No. 2. — Do., with Focussing 

 Screen and Double Dark 

 Slide 16s. 6d. 



Xo. 3.— Do. do.(3isq.) 31 s. 6d. 



-\dapting either to fit Micro 

 scope ...9d. 



Brass Adapter, do. ... 3s. 6d. 



No. 3, Ijeing of I-anlern ,Si/c, ib einiTteiitly 

 adapted for 

 making direct 

 contact Micro- 

 L a n t e r ii 

 Slides. 



Science Gossip says : — " From a personal experience we can vouch for the 

 fact that it is capable of doing fairly critical work, and it is therefore 

 specially suitable for students in the photographing of botanical, 

 entomological and histological specimens." 



K/to7i'iciif:e UMicrosci^/tical Editor) says : — " I have seen this class of 

 camera vised by ardent photographers who have wished to secure a 

 photograph of a iiniiiue or interesting specimen." 



JOHN BROWNING!;Ss;^S^x''fS^d^S? LONDON. 



Estab. 17e.=. 



■ ■Optician, 72 New Oxford St. 



I . !. Xo 



THE 



English Mechanic 



WORLD OF SCIENCE 



Commences with Volume C I 

 its Second Century. 



For fifty years it has steadily and continuously broadened 

 the bounds of its influence, and yearly added to the ranks 

 of its thousands of voluntary helpers. We ask to-day, not 

 for conscription, but for universal voluntary service in the task 

 of enlisting the young in the service of science. It is no duty 

 of ours to disc\iss whether we were ready as a nation for the 

 srreat struggle in which the Briti'^h Empire is engaged : but 

 it is no secret that, after a generation of universal elementary 

 education, the niajoritv of our countrymen grow into man- 

 hood and womanhood ill equipped for the industrial struggle 

 with their competitors of better-trained nations, and content 

 to seek recreation in vicarious athletics and the unedifying, 

 hut exciting, "popular" literature of the time. Of hundreds 

 of thousands of these it is the bare truth to say the fault 

 is not theirs, but that of their teachers. If youth were but 

 led jiid'ciou'-lv, and without pedantry, to the realisation 

 of the plej-sures of science, aptitude and inclination would 

 attract yearly increasing thousan Is to the profitable utiUsation 

 thereof in manhood One proof that this is so is the eagerness 

 with which the English Mechanic is read in schools where 

 the tencbers have familiarised the children with its contents, 

 \\'ill more teachers make The English Mechanic and World 

 OF Science tbeir school book ? If so, thousands of men and 

 women who will read if^ pages tifty years hence will gratefully 

 remember them. ^^^^__^^^^^^^«^ 



A Specimen Copy will be sent free to any address 



on reciiiest. 



ENGLISH MECHANIC, 



5. EFFINGHAM HOUSE, 

 ARUNDEL STREET. STRAND. LONDON, W.C. 



