proceedings: philosophical society 251 



Mr. C. G. Abbot presented a paper entitled, Experiments in meas- 

 uring solar radiation from halloons. The author stated that close agree- 

 ment had been obtained in spectro-bolometric determinations of the 

 solar constant of radiation at four stations; the mean result of about 

 700 independent determinations is 1.93 calories per sq. cm. per minute. 

 Although these results depend on estimates of the transmission of the 

 atmosphere, the diversity of the circumstances of the observations 

 is such that the agreement of results strongly indicates their accuracy. 

 It is, however, maintained by some that the work is wholly unsound, 

 and that the real solar constant value is 3.5 calories per sq. cm. per 

 minute or more. Accordingly, a recording pyrheliometer has been 

 devised for use with sounding balloons. It is modified from the silver- 

 disk pyrheliometer now in general use. A blackened disk, lying hori- 

 zontally, is alternately exposed to the sun and shaded by a conical 

 reflecting shutter at four-minute intervals. A thermometer whose 

 reading is photographically recorded measures the rise and fall of the 

 temperature of the disk. A barometric element records pressure of 

 the atmosphere. Five ascents were made from Avalon, California, in 

 1913, and three ascents from Omaha in 1914, by cooperation with 

 the United States Weather Bureau. All instruments were recovered. 

 The most successful flight, at noon on July 11, 1914, reached an altitude 

 well above 20,000 meters. Three excellent records of solar radiation 

 were secured near maximum elevation, where the barometric pressure 

 is less than -jV of that at sea-level. These results are in good agreement, 

 and (reduced to mean solar distance) yield a mean value of 1.85 calories 

 per sq. cm. per minute. It is thought that about 2 per cent should 

 be added for the efl"ect of the remaining air, making the value 1.89 

 for this day. Its probable error is about 3 per cent. The paper was 

 discussed by Mr. White as to the effect of the downward current of 

 air in balloon w^ork; by Mr. Woodw^ard, who questioned the usual 

 method of estimation of the quantity of the atmosphere above any 

 level; and by Mr. Lambert with reference to the grounds upon which 

 certain investigators base a value pf the solar constant at a value near 

 4 calories. 



Mr. R. S. Woodward then presented a paper on The compressibility 

 of the earth's mass, in which he considered the problem of the radial 

 compressibility of the earth's mass due to change in internal or to 

 surface stress. Assuming this mass to be spherical and that its den- 

 sity is a function only of distance from the center, the variation in 

 length of the radius due to condensation (or dilatation) was shown 

 to be equal to the volume-integral of the condensation divided by the 

 area of the sphere. Application was made of the law of condensation 

 defined by Laplace's hypothesis connecting density and stress in any 

 mass. Using round numbers, this hypothesis leads to the conclusion 

 that if the pressure of the atmosphere were doubled, the radius of the 

 earth would be diminished by two meters. The importance of this 

 conclusion in geology especially was emphasized. 



J. A. Fleming, Secretary. 



