Mabch 6, 1914] 



SCIENCE 



347 



Algeria, it appears that a lone; period fluc- 

 tuation is associated with the sun-spot 

 numbers. This connection is brought out 

 by taking the mean monthly values of the 

 solar constant measurements at Mount 

 Wilson from the year 1906 on, and com- 

 paring them with the mean monthly sun- 

 spot numbers of Wolf er for the same period. 

 From such a comparison it appears that 

 the greater number of sun-spots the higher 

 will be the solar constant of radiation, and 

 that an increase of a hundred sun-spot 

 numbers corresponds to an increase of 

 about 0.07 calories per square centimeter per 

 minute in the solar radiation outside the 

 earth's atmosphere. This is a very curious 

 circumstance, when it is recalled that the 

 temperature of the earth is generally lower 

 at sun-spot maximum than at sun-spot 

 minimum, notwithstanding that, if the 

 above result be true, the solar radiation is 

 more intense at sun-spot maximum than 

 at sun-spot minimum. On the other hand, 

 the result is in line with the irregular 

 variability of the Myra type of variable 

 stars. 



ATMOSPHERIC TRANSMISSION 



In connection with the measurements 

 which have been made of the solar constant 

 of radiation, there have been some inter- 

 esting by-products. Among these we may 

 mention first the determination of the 

 transmission coefficients of the earth's 

 atmosphere for light of all wave-lengths, 

 including the ultra-violet and the infra-red 

 spectrum, and ranging from wave-length 

 0.3 IX in the ultra-violet to wave-length 2.5 ^i 

 in the infra-red. These transmission 

 coefficients have been obtained by the 

 Smithsonian observers at Washington, 

 Mount Wilson, Mount Whitney and Bas- 

 sour. It is very interesting to compare 

 them with the transmission of the atmos- 

 phere as computed according to the theo- 

 retical consideration of Rayleigh on the 



cause of the light of the sky. It is found 

 that by means of these observed transmis- 

 sion coefficients the value of the number 

 of molecules in the atmosphere may be ob- 

 tained almost as accurately as by the use 

 of the more common laboratory methods 

 for determining the number of molecules 

 per cubic centimeter of a gas of known 

 density. It is found that the theory of 

 Rayleigh connecting the change of trans- 

 mission with the wave-length is closely con- 

 firmed by the observations at Bassour, 

 Mount Wilson and Mount Whitney. Simi- 

 lar measurements of atmospheric trans- 

 mission for more limited regions of the 

 spectrum have been made by other ob- 

 servers at high altitudes, and these also 

 are found to agree closely with the theory 

 of Rayleigh, and with our own observations. 

 Not less interesting is the determination 

 of the distribution of energy in the sun's 

 spectrum, and thereby of the probable tem- 

 perature existing in the sun. The solar 

 temperatures may be inferred also from the 

 value of the solar constant of radiation 

 itself, and the two methods agree substan- 

 tially in giving the probable solar tempera- 

 tures as between 6,000 and 7,000 degrees 

 absolute centigrade. 



RECENT BALLOON EXPERIMENTS 



Notwithstanding the satisfactory state 

 of the theory of solar constant measure- 

 ments by the method of Langley, depend- 

 ing upon spectro-bolometric observations 

 at high and low sun combined with meas- 

 urements by the pyrheliometer, and not- 

 withstanding the close agreement between 

 results obtained by this method for many 

 years at stations of differing altitude from 

 sea-level to 4,420 meters elevation, there 

 still exists the possibility that if we could, 

 indeed, go outside the atmosphere alto- 

 gether we should obtain values differing 

 materially from those above given. So 



