NOVBMBEK 6, 1914] 



SCIENCE 



673 



ment of our robust and practical ideals, can 

 be gained by the study of the work of Faraday, 

 Newton, Kepler, Franklin, Darwin and Pas- 

 teur, and the general conceptions on wMcli 

 their work was based. 



In conclusion one must recognize that sci- 

 ence is international, English, German, 

 French, Italian, Russian, all nations coopera- 

 ting in the interests of racial progress. Ac- 

 cordingly, a survey of the sciences tends to in- 

 increase mutual respect, and to heighten the 

 humanitarian sentiment. The history of the 

 sciences can be taught to people of all creeds 

 and colors, and can not fail to enhance in the 

 breast of every young man or woman, faith in 

 human progress and good will to all mankind. 

 Walter Libby 



Carnegie Institute op Technology. 



some inconsistencies in physics text-books 

 The following is a quotation from Kohl- 

 rausch's " Physical Measurements " : 



The coefficient of capillarity may be de-fined as 

 the weigit of fluid which is supported by the unit 

 of length of the line of contact of its surface 

 ■with a thoroughly wetted plate. 



Now a coefficient is a proportionality factor, 

 a pure number expressing the measure of some 

 specified force or property. For example, the 

 volume coefficient of expansion of a gas is 

 the ratio between the increase in volume per 

 degree rise in temperature, and the volume at 

 zero degrees centigrade, the pressure remain- 

 ing constant. If we keep the expression coeffi- 

 cient of capillarity or capillary constant it 

 must be as the ratio between the weight of 

 liquid raised above the undisturbed level and 

 the length of the line of contact of its surface 

 with a thoroughly wetted plate. 



In my opinion there is a difficulty with 

 ratios involving quantities measured in differ- 

 ent units. It is much simpler, for instance, 

 to grasp the significance of the ratio of the 

 extension of a wire per given or unit tension, 

 to the initial length (see Duff's " Text-book 

 of Physics," p. 122) than of Young's modulus 

 expressed as the ratio of the longitudinal 

 stress to the longitudinal strain; the stress 



measured as tension per unit cross section and 

 the strain as extension per unit length. 



The quotation from Kohlrausch is not in 

 any ease a definition: it explains how the 

 surface tension of a liquid may be measured. 

 Capillarity is the phenomenon of rise or fall 

 of liquids in tubes due to the surface tension 

 of the liquids. In most recent text-books and 

 laboratory manuals the term coefficient of 

 capillarity, capillary constant or coefficient of 

 surface tension is not used. Duff, for instance, 

 and Ames in his " College Physios," state this : 



If a line be imagined drawn along the surface of 

 a liquid, the part of the surface on one side of the 

 line pulls on the part on the other side, and if the 

 length of the line be supposed one centimeter the 

 pull in dynes ds taken as the magnitude of the 

 surface tension of the liquid. 



Another term used inconsistently is specific. 

 A specific quantity is concrete and so should 

 be expressed in a unit. But we find specific 

 gavity defined as a ratio. 



The specific gravity of a body is the ratio of 

 the mass of any volume of it to the mass of the 

 same volume of pure water at 4° C. (Carhart's 

 "College Physics"). Specific gravity may be de- 

 fined consistently as the weight of unit volume of 

 the substance (Watson 's ' ' Text -book of Physics " ) . 

 But it is useful to keep in the defijiition, because 

 of our methods of determining specific gravity, the 

 idea of comparison. Kimball ("College Phys- 

 ics") calls it relative density, defining it as "the 

 ratio between the density of the substance consid- 

 ered and the density of a standard. ' ' 



The definition of the specific heat of a sub- 

 stance is consistently given, in most recent 

 text-books, as the quantity of heat in calories 

 which will raise the temperature of one gram 

 of a substance through one degree centigrade. 

 The specific inductive capacity of a medium is, 

 however, defined as the ratio between the 

 capacities of two condensers equal in size, one 

 of them being an air condenser, the other 

 filled with the specific dielectric. But this 

 ratio is as often called dielectric constant, 

 sometimes the coefficient of induction. 



These points are small ones, but they are 

 puzzling to beginners and always annoying. 

 Sue Avis Blake 

 Smith College 



