PHYSICS. 313 



reduces to the cylindrical pattern, in which the movable cylinder may 

 be within or without the fixed cylinder. If the cylindrical mantle is 

 removed the instrument is of the disk form, the simplest case of which 

 is the absolute electrometer. All of these instruments may, with 

 less sensitiveness, be used idiostatically. None of them, however, 

 is exceptionally sensitive, the disk form (which is most sensitive and 

 at the same time most treacherous) being characterized by a dis- 

 placement of about 10"^ centimeter per volt, in favorable cases. Far 

 greater sensitiveness is therefore secured by adapting the device of two 

 small light parallel mirrors for the measurement of angle (as referred 

 to above) to the needle of the quadrant electrometer. When this is 

 properly done, an instrument capable of measuring 10 to 20 millionths 

 of a volt per vanishing interference ring may be constructed, pro- 

 vided a satisfactory environment is at hand. The chapter also 

 contains a great variety of experiments with each of these forms of 

 apparatus. 



Hayford, John F., Northwestern University, Evanston, Illinois. Grant 

 No. 776, allotted December 15, 1911. Investigation of the laws of 

 evaporation and stream flow. $2,000 



The general plan of the investigation of evaporation is to consider 

 each of the Great Lakes in turn as an evaporation pan, to evaluate 

 the income, outgo (other than evaporation), and change of content 

 of the lake, day by day, as accurately as possible, and from these 

 evaluations to determine the daily evaporation and its relation to 

 meteorological conditions. When sufficient progress has been made 

 in the study of evaporation it is proposed to apply the knowledge thus 

 gained to the investigation of the laws of stream flow in the United 

 States. The progress made to date in the evaporation investigation 

 has been satisfactory. Various difficulties have been encountered and 

 overcome. No insuperable difficulties have appeared. It would be 

 premature yet to report in detail the items of progress made or to 

 estimate the degree of success that will probably be attained in the 

 investigation. No attempt has thus far been made to study stream 

 flow, as that portion of the study is intended to be based on more 

 information in regard to evaporation than is now available. 



Howe, Henry M., Columbia University, New York, N. Y. Grant No. 

 877, allotted March 21, 1913. Study of the life history of the constitu- 

 ents of carbon steel, etc. (For previous reports see Year Books Nos, 

 6-11.) $500 



The upper limit of the transformation range of the iron-carbon 

 alloys has been determined in a series of 19 steels varying in carbon 

 content from 0.03 per cent to 1.43 per cent, and in special cases 

 varying also in manganese content and in phosphorus content, by 



