468 



SCIENCE 



[N. S. Vol. XXIX. No. 742 



Some Data regarding Recent Magnetic Storms: 

 L. A. Bauee, Carnegie Institution, Washing- 

 ton. 



Renewed interest was recently shown in mag- 

 netic storms on account of severe ones last Au- 

 gust and September and because of Hale's dis- 

 covery of the Zeeman magnetic effect in sun-spots. 

 Some concluded that a true explanation of the 

 origin of terrestrial magnetic storms had been 

 found. However, a simple calculation shows 

 that the magnetic field intensity observed in 

 fiim-spots is totally inadequate to affect the most 

 sensitive magnetic instruments. Whereas the 

 effects actually observed during storms exceed 

 many times — in fact a hundred fold and more — 

 the limit of measurement (about 1/100,000 

 C.G.S unit). Little progress has been made in 

 the solution of the problems presented by mag- 

 netic storms, one reason being that the investiga- 

 tions to be thorough are beyond the power of the 

 average individual. They must, hence, generally 

 be restricted either to one particular phase or to 

 one element — usually the change in the compass 

 direction. An important question is that of the 

 seat of the forces regarded as causing the ob- 

 eerved effects; whether it be above the earth's 

 surface or below, or even of combined origin. 

 Another fundamental question is, whether an 

 actual change of magnetization in addition to a 

 shift of the magnetic axis takes place, and if so 

 its magnitude and duration. In the case of the 

 very notable storm of October 31-November 1, 

 1903, it would appear as though an actual 

 diminution of the earth's magnetic moment oc- 

 curred which continued almost for two months 

 after the apparent cessation of the storm. Sim- 

 ilar calculations are in progress regarding the 

 more recent storms. 



Optical Properties of Electrolytic Films of Iron, 

 Viclcel and Cohalt: C. A. Skinneb and A. Q. 

 Tool, University of Nebraska. 



.4.??. Absolute Gauge for Measuring High Hydro- 

 static Pressures: P. W. Bbidgman, Harvard 

 University. 



The pressure range over which it has been 

 hitherto possible to measure various physical 

 effects of high pressure has been restricted by the 

 fact that the common forms of pressure gauge 

 leak at very high pressures. Tlie best known 

 work in this field has been that of Amagat, who 

 worked to about 3,000 kgm. per sq. cm. This is 

 the working pressure in modern high power ar- 

 tilleiy. The essential parts of all gauges for 

 these high pressures are a piston fitting a 



cylinder so accurately that the friction between 

 them is small and at the same time the leak past 

 the piston is very slow. At high values of pres- 

 sure the leak becomes so rapid that it is impos- 

 sible to make measurements. In this paper a 

 form of the usual gauge was described in which 

 the cylinder is made to shrink automatically by 

 the pressure, so that the leak remains slight 

 even at very high pressures, while the freedom of 

 motion of the piston is not impaired. With this 

 gauge pressure measurements accurate to .1 per 

 cent, have been made to nearly 7,000 kgm. per 

 sq. cm. At higher pressures other parts of the 

 apparatus break. This is not the limit of the 



The Resistance of Mercury as a Secondary Gauge 

 for High Pressures: P. W. Bbidqmaj^, Harvard 

 University. 



In practical use the above form of gauge is 

 inconvenient because it is slow and unwieldy. 

 In this second paper measurements of the elec- 

 trical resistance of mercury under pressure are 

 given from which the pressure may be calculated 

 if the change of resistance is known. Electrical 

 resistance is very easy to measure, and it is pro- 

 posed that in practise pressure be measured in 

 this indirect way. The accuracy attainable is .1 

 per cent. The total change of resistance for 

 7,000 kgm. is about 20 per cent. As one would 

 expect, the change in the resistance effected by 

 pressure is less when pressure is high, as is also 

 the change brought about by temperature change. 

 The change of resistance is about ten times the 

 change of volume produced by a corresponding 

 pressure. 



Methods for Measuring Compressibilities at High 

 Pressures: P. W. Bbidgman, Harvard Univer- 

 sity. 



In this paper methods were described for meas- 

 uring the cubic compressibility of solids or of 

 liquids at these high pressures. Measurements 

 were made of several samples of steel, glass and 

 aluminum. The values for steel fall between the 

 two best previous determinations, which differ by 

 100 per cent. The other values agree with the 

 commonly accepted results. The accuracy of the 

 method is about .35 per cent., considerably higher 

 than the best previous determinations. The only 

 liquid measured was mercury. In only one in- 

 stance has this been measured before to more 

 than 500 kgm., when measurement was made to 

 3,000 kgm. The value found in this work agrees 

 with former values, except that the change of 



