SCIENCE— ADVERTISEMENTS 



OUGHTRED'S 



Mathematical Symbols 



By FLORIAN CAJORI 



RECENT PUBLICATIONS 



A List of Oughtred's Mathematical Symbols 



with Historical Notes. Bj' Florian Cajori .25 



On the History of Gunter's Scale and the 

 Slide Rule during the Seventeenth Cen- 

 tury. By Florian Cajori 35 



Treatment of Harmonics in Alternating Cur- 

 rent Theory by means of a Harmonic Al- 

 gebra. By Abraham Press 1.00 



A New Morphological Interpretation of the 

 Structure of Noctiluca, and its bearing on 

 the Status of the Cystoflagellata (Haekel ). 

 By Charles A. Kofoid 25 



Classification of Involutory Cubic Space 



Transformations. By F. M. Morris ... .25 



The University of California Press 



Berkeley, California. 280 Madison Ave., New York 



We Announce 



NEW GEOGRAPHY 

 BOOK TWO 



(Frye-Atwood Geographical Series) 



The first textbook to supply 

 a full set of maps to illustrate 

 the new regional method of 

 teaching geography. They 

 represent the last word in the 

 map-making art. They must 

 be seen to be appreciated. 



GINN AND COMPANY 



70 Fifth Avenue NEW YORK 



t t 



THALOFIDE CELL" 



A NEW LIGHT REACTIVE RESISTANCE 

 OF GREAT SENSITIVITY 



These new cells will lower their electrical resistance 50 per cent. 



on exposure to .25 of a foot candle when the source used is a 



Tungsten Filament. Special cells are constructed which will do 



this in .06 of a foot candle. 



Their recovery after exposure is extremely rapid as also is 

 their response to the light stimulus which 

 is in marked contrast to the Selenium Cell, 

 especially on exposure to very low light 

 intensities. 



Write for Partienlars 



Case Research Laboratory 



AUBURN, NEW YORK 



