DEPARTMENT OF TERRESTRIAL MAGNETISM. 295 



work can not be done until suitable paramagnetic crystals are pre- 

 pared, but with an apparatus soon to be completed, some related work 

 can be done in the very near future. 



Investigation of the effects hitherto studied under the caption of magnet- 

 photography. — A somewhat extended investigation has been made 

 under definite and controllable conditions, and evidence has been 

 obtained against any effect of the magnetic field. An abstract of this 

 work is given on pages 304-306. 



Investigation of the rotation produced by magnetization and magnet- 

 ization produced by rotation. — Experiments with iron and nickel have 

 shown the rotation effect looked for, but with disturbances too great 

 to make useful measurements possible. Lack of mechanical assistance 

 and difficulty in getting material have made progress extremely slow. 

 It is hoped ultimately, wdth apparatus now in course of construction, to 

 get satisfactory results wdth iron, nickel, and cobalt. 



Further preparations have been made for the experiments on mag- 

 netization by rotation, to be performed in the Experiment Building. 

 In connection with this work, a special fluxmeter is in process of con- 

 struction. It is possible that this instrument can also be made useful 

 in measuring the changes in horizontal and vertical intensities. It is 

 hoped to install this apparatus before long in the experiment building. 

 Report on electromagnetic induction. — This report was prepared for 

 and presented at the Cornell University Physics Conference and 

 Reunion held in connection with the semi-centennial celebration, and 

 will be presented at the coming joint meeting of the American Physi- 

 cal Society and the American Institute of Electrical Engineers. (See 

 abstract, p. 306.) 



Course of 26 lectures on theories of magnetism. — This was given weekly, 

 with certain interruptions, at the Laboratory, between September 30, 

 1918, and June 9, 1919. 



Those chiefly engaged on the above researches were: S. J. Barnett 

 (chief of division), D. M. Wise, and C. A, Kotterman. 



Apparatus for determining the acceleration of gravity at sea, by S. J. 

 Barnett and H. R. Grummann. — With the hope of producing, if possible, 

 an apparatus for the precise determination of gravity at sea, all the 

 methods hitherto proposed were examined, with the result that the 

 constant-volume, constant-temperature, gas-thermometer method was 

 fixed upon as being the most promising. Various modifications of this 

 method have been used by Mascart, Hecker, Briggs, and Duffield. 

 The apparatus of Duffield, which has the advantages of approximate 

 independence of minute temperature variations and of a possible 

 considerable magnification of sensitiveness, was adopted with certain 

 modifications, partly suggested by Duffield, and partly suggested by 

 Schuster on the basis of an elaborate theoretical study. A tube of this 

 design has been constructed from glass of a kind largely free from after- 



