KNOWLEDGE. 



March. 1915. 



SMALL SPECTROSCOPES. 



SOLAR RROMIMBMCE SRECTROSCORES ifor .ul.iptafion to a„v 7V/c-.scoy.f;. 



This instrument clearly shows the solar prominences and often bright reversals of the C line. Mounted on a tube, or 

 astronomical thread to suit customers own instrument. 



PRICE, with au.xiliary telescope for specially observing the C line ... ... ... £5 O O 



Without auxiliary telescope ... ••• ••• •■■ ••• ••• ~* ** ^ 



The .,li,>>e pii.cs include .id.iplation. but orders should be accompanied by an eyepiece from the telescope with which it is to be used. 



DIRECT VISION SRECTROSCORES. 



These Spectroscopes have been brought to a verv high state of perfection, and are particularly suitable for .\bsorption, 

 Rainband, and Emission Spectra. The S-^-in. can be fitted with an Interference Etalon showing the Fabry and Perot ring 

 system and subjecting the mdividual linesof the Spectrum to a resolving power of about 100,000. The Zeeman effect can 

 also be detected on suitable radiations (such as the yellow Helium line), a distinct tripling of the line being visible. 



F.ABRY 



-AND 



PEROT 



RING 



SYSTEM. 



PRICES : No. 5— 5i-in. 



£2 10 O 

 £1 3 O 

 £2 O O 



with high-dispersion prism and adjusting slit, in case ... 

 Etalon attachment for above 

 No, 4 — 3i-in, with high-dispersion prism and adjusting slit, in case ... 



RAMSAY SPECTROSCOPES, i i r.i|jid examination of vacuum tubes, 15/- and 20/- e.ach. 



OISTANT VISION SPECTROSCOPES* a cheap instrument for rapid spectroscopic observation of Spark, .Arc or other light sources which, when 

 used ironi any distance over two yards, are point sources. PRICE, incase, £"1 2 6> 



Send for Illustrated Leaflets and Price Lists. 



ADAM HILGER, Ltd., 75a, Camden Road, London, N.W. 



Tde^raphic Add, 



■ Si'iiLKici 1 ■. , Camko.^ii. London. 



l\kph ■■:,■ \-nd' 



Index of Spectra 



NEW SERIES. 



Designed to complete and bring up to date 

 the Index of Spectra and previous Appendices. 



Appendix V contains Air, Aldebaranium, Aluminium, 

 .\lumina. Ammonia, Antimony, Argon, Arsenic, 

 Barium, Beryllium, Bismuth, Boron. Bromine, 

 Cadmium, Caesium, Calcium. Carbon, Cassiopeium, 

 Cerium, Chlorine, 12s. 6d. 



Appendix W contains Chromium, Cobalt, Copper, Dys- 

 prosium, Erbium, Europium, Fluorine, and ".\dditions 

 and Corrections to .\ppendix V." 12s. 6d. 



From " Nature," December 11th. 1913 : — 



" ' Watts' Index of Spectra.' — Yet another 

 series of Appendices to this most valuable com- 

 pilation of wave-length data has been commenced 

 by the publication of Appendix V." 



Post free from the .Author: 



Dr. W. MARSHALL WATTS, 



"Shirley," Venner Road, Sydenham, London, S.E. 



The Leading Journal of Science. 



SIXPENCE WEEKLY. 



All who are convinced of the importance 

 of scientific principles being brought into 

 operation in all branches of our national 

 life should read NATURE regularly, for 

 this view has been steadily maintained in 

 the journal from its foundation. 



*,* Many of the recent numbers contain 

 articles of topical scientific interest. 



SUBSCRIPTIONS. 



Great Britain and Ireland. 



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



Quarterly 7s. 6d. 



Abroad. 



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



Quarterly 8s. 



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



