PHYSICS, 337 



The fringes here in question are preferably the very luminous achro- 

 matic fringes. They have been identified as ultimately colors of thin 

 plates, but thej'' look like Fresnel's fringes. In connection with this 

 work, however, another type of fringes was detected, obtainable 

 with a fine sUt, white Ught, and in case of centered spectrum fringes 

 when the ocular of the telescope (or the eye) is out of focus. These 

 are actually Fresnellian interferences, but being made up of broad 

 concentric hyperbolic areas, brilliantly complementary in color, they 

 resemble the lemniscates of biaxial crystals without the shadows. 



Ha3rford, John F., Northwestern University, Evanston, Illinois. Investiga- 

 tion of the laws of evaporation and stream-flow. (For previous reports see 

 Year Books Nos. 12-15.) 



Professor Hayford's report covers the period from August 1, 1916, 

 to July 31, 1917. But Uttle progress was made during the year, due 

 to the indirect influence of war conditions, and the expenditures were 

 correspondingly small. The progress stopped entirely in June 1917, 

 since which time he has been engaged in certain scientific work con- 

 nected with the Government in addition to his regular college duties. 

 The progress made was principally a direct continuation of that indi- 

 cated in the annual report for the period August 1, 1915, to July 31, 

 1916. Nothing especially new was developed, though real advance was 

 made in securing increased accuracy and in confirming earlier con- 

 clusions. 



The computers during the year were, F. D. Danielson, J. A. Folse, 

 T. Doll, R. M. Quirk, M. F. Hayford, F. Mohr, A. McMurdie, H. G. 

 Bersie, and C. W. Froehlich. Over 90 per cent of the computing was 

 done by four of these men, Messrs. Danielson, Folse, Doll, and Quirk. 



Howe, Henry M., Columbia University, New York, New York. Research 

 associate in metallurgy. (For previous reports see Year Books Nos. 6-15.) 



During the year 1916-1917 I have explained the abruptness of the 

 transition from the columnar to the equiaxed structure in slowly 

 solidified masses of metals and other substances, including rocks, as 

 representing the moment when the thermal gradient in the region in 

 which sohdification is occurring becomes so flat that the less fusible 

 molten matter at a material distance from the face of the already 

 sohdified walls now sohdifies before the more fusible layer of molten 

 in immediate contact with those walls, made more fusible by the selec- 

 tion in solidification. Up to this moment solidification has occurred 

 at the tips of the columnar crystals forming the now solid walls, and 

 hence has been columnar. From this moment it occurs about nuclei 

 disconnected with those columns. 



I have investigated the laws and explanations of ''grain growth," 

 i. e., the increase in size of the individual allotriomorphic crystals of 



