February 28, 1919] 



SCIENCE 



215 



This metal has already been applied in a 

 number of cases to commercial devices for 

 this purpose, one of which is being manu- 

 factured at the present time by tho Central 

 Scientific Company. 



Any increase of sensitiveness, or any reason- 

 able amount of force on a given temperature 

 change may be obtained by manipulation of 

 the length, width and thickness of the metal. 

 By using very thin sections extreme sensi- 

 tivity may be obtained, deflections as great as 

 one fourth inch per degree Centigrade being 

 possible. On the other hand, by materially 

 increasing the thickness great force can be 

 created, in one instance approximately one 

 fourth ix)imd per degree Centigrade. 



On account of the process of manufacture 

 employed, the danger of permanent set has 

 been practically eliminated, so long as the 

 metal is not overstrained. 



G. E. Thermostatic Metal, as it is known to 

 the trade, is produced regularly in thicknesses 

 from .015 to .25 inch; widths up to 6 inches 

 and lengths up to 30 inches. In special cases 

 it may be obtained in thickness as small as 

 .005. 



I feel sure that a knowledge of the char- 

 acteristics and adajitability of this material 

 will enable many experimenters to solve prob- 

 lems of temperature control or indication with 

 much greater ease and accuracy than hereto- 

 fore. Chester I. Hall 



General Electric Company, 

 Fort Wayne, Ixd. 



common numerals 

 The origin of our common number symbols 

 has never been clearly established, but until 

 recently all writers on this subject agreed 

 that these symbols were transmitted to Eu- 

 rope by the Arabs who had obtained them 

 from India. This is the view expressed in 

 the general encyclopedias and in our mathe- 

 matical histories which consider this question. 

 For example, in the eleventh edition of the 

 Britannica under the word "numeral" there 

 appears the following statement; 



The areas designated by states appear in the 

 following table: 



What is quite certain is that our present decimal 

 system, in its complete form, with the zero which 

 enables us to do without the ruled columns of the 

 abacus, is of Indian origin. Prom tho Indians it 

 passed to the Arabians, probably along with the 

 astronomical tables brought to Bagdad by an In- 

 dian ambassador in 77.3 a.d. 



In view of these facts it is very interesting 

 to note that during recent years available data 

 relating to the origin of our common number 

 symbols have been carefuly reexamined by 

 Carra de Vaux, who published in volume 21 

 of Scieiitia a brief summary of his results. 

 Among the most surprising of these results 

 arc the following: Our common number 

 symbols originated in Europe and from there 

 were transmitted to the Persians. Both India 

 and Arabia received them from Persia, so that 

 the common term Hindu-Arabic numerals is 

 decidedly misleading. The conurion numerals 

 did not come from letters of the alphabet, but 

 were formed directly for the purpose of repre- 

 senting numbers. 



It does not appiear likely that all of these 

 conclusions reached by Carra de Vaux, who 

 has made an extensive study of the intellec- 

 tual life among the Mohammedans, will be at 

 once accepted, but they tend to exhibit the 

 weak foundation upon which the history of 

 our common numerals has thus far rested. 

 In fact, the nature of this question is such 

 that it seems likely that general agreement 

 as regards the origin of our numerals can 

 result only from that attitude of mind (known 

 as philosophy) which would rather accept as 

 facts what can not be proved than acknowl- 

 edge ignorance. Conclusions similar to those 

 of Carra de Vaux were also expressed in a 

 Russian work by N. Bubnow (1908), which 

 was translated into German and published in 

 Berlin in 1914. G. A. Miller 



PSYCHOLOGICAL RESEARCH FOR AVIATORS 



To THE Editor of Science: In his article 

 on " Psychological Research for Aviators " in 

 Science of January 24 Dr. Duiilap inadvert- 

 ently neglects some of the most imiwrtant 



