234 REPORTS ON INVESTIGATIONS AND PUOJECTS. 



To test some of the equations deduced, it is necessary to know the index 

 of refraction of the glass of the grating for all wave-lengths. Hence the 

 author has spent considerable time in devising methods by which the refrac- 

 tion of plate glass may be found in all parts of the spectrum, by a general 

 procedure, in which total reflection is combined with diffraction. This has 

 been worked out with a degree of precision corresponding to its probable 

 importance in practical work. 



The dependence of the size and color of coronas on the thickness of the 

 cloud-layer producing the display was tested by a sensitive method, in which 

 the coronas due to different thicknesses of layer could be superposed. No 

 difference of character could be detected, a result of importance in connec- 

 tion with the theory of coronas. 



In relation to the occurrence of vapor nuclei in dust-free wet air, the 

 author has constructed a small type of fog chamber, by which such nuclei 

 may be caught to the number of several million per cubic centimeter and of 

 a corresponding degree of small size. 



The author has, moreover, returned to the moot subject of persistent nuclei 

 produced by the X-rays, or any other sufficiently intense cause of ionization, 

 with a view to determining the density of ionization which must be produced 

 if persistent nuclei are to appear. It was found that the number of ions 

 must exceed at least 300,000 per cubic centimeter to be accompanied by per- 

 sistent nuclei. If we imagine the ionization to be under its own specific 

 kinetic pressure, then if this reaches a definite value a kind of condensation 

 occurs very similar to the case of a vapor, and the persistent nuclei are the 

 result. 



Finally, the author has made a large number of experiments on the diffu- 

 sion of gases through liquids in the elucidation of more remote parts of the 

 present subject. 



Howe, H. M., Columbia University, New York, New York. Grant No. 698. 

 Determination of the refining temperature of steel. (For previous re- 

 ports see Year Books Nos. 6-9.) $500 



Steel in its slowly cooled state (the state in which it is used for structural 

 purposes, rails, beams, boiler and ship plates, etc.) is a granitic or con- 

 glomerate mass, consisting of (i) pearlite, a eutectoid mechanical mixture 

 of particles of nearly pure metallic iron called ferrite, and the iron carbide 

 FegC called cementite; and (2) of masses of either this ferrite or this 

 cementite in a free state ; i. e., not intertwined as pearlite. In hypo-eutectoid 

 steels, i. e., those with less than about 0.90 per cent of carbon, the con- 

 glomerate consists of pearlite with free ferrite ; in hyper-eutectoid steels, 

 i. €., those with more than about 0.90 per cent of carbon, it consists of 

 pearlite with free cementite. 



When such steel, whether hypo-eutectoid or hyper-eutectoid, is heated up 

 through a certain critical or transformation range, of which the lower 



