June 21, 1918] 



SCIENCE 



609 



ceed Professor A. G. Smith, whose death oc- 

 curred in the fall of 1916. 



Appointments at Cornell University have 

 been made as follows: F. K. Richtmyer, pro- 

 fessor of physics; John B. Bentley, jr., pro- 

 fessor of forestry; Charles L. Gibson, professor 

 of surgery, to succeed the late Professor Stim- 

 son ; John A. Hartwell, associate professor of 

 surgery and William C. Thro, professor of 

 clinical pathology. Medical College, New York. 



William S. Taylor, acting professor of 

 rural education at Cornell University, has 

 been appointed professor of agricultural edu- 

 cation at Pennsylvania State College. 



Dr. a. R. Cushnv, F.R.S., professor of ma- 

 teria mediea and pharmacology in the Uni- 

 versity of London (University College) since 

 190.5 has been appointed to the chair of materia 

 mediea in the University of Edinburgh. Dr. 

 Cushny was professor of pharmacology in the 

 University of Michigan from 1893 to 1905. 



DISCUSSION AND CORRESPONDENCE 



PYRHELIOMETRY AND SOLAR RADIATION 



To THE Editor of Science : I hope it may 

 interest your readers, and more fully explain 

 the discrepancy between Professor Bigelow's 

 work and mine, if you can find space for the 

 accompanying letter. 



May 14, 1918 

 My dear Professor Bigelow: 



1. I received yesterday from your publishers a 

 complimentary copy of your new book entitled 

 ' ' Treatise on the Sun 's Radiation. ' ' You are kind 

 to have it sent to me. 



2. I received to-day your communication on a 

 26.68-day solar synodic period. 



3. Some time ago I received some other data 

 from you relating to observations and computa- 

 tions of radiation. 



4. While I appreciate your kindness in remem- 

 bering me personally, I am obliged to tell you that 

 I can not at all accept your views and I do not 

 think you either fully understand or fairly weigh 

 our work. My reasons are partly given below. 



5. Among the words you use most is ' ' Pyrheliom- 

 eter. " We carefully made and standardized 

 Silver Disk Pyrheliometer S. I. III., at your re- 

 quest, and sent with it an accurate description of 

 the method by which it must be read and reduced 

 in order to give results to correspond with its con- 



stant of calibration. In your book "Atmospheric 

 Circulation and Radiation," pages 263 to 267, I 

 am surprised to see that you describe and prescribe 

 another method of using it whereby it can not give 

 results agreeing with its constant of calibration. 



6. You use this word "Pyrheliometer" and its 

 modifications often very objectionably when you 

 mention our work. You make it appear as if we 

 attach weight to empirical processes of extrapola- 

 tion of total radiation of all wave-lengths com- 

 bined. If an observer could operate on the moon, 

 a pyrheliometer would be a very much more valu- 

 able instrument than it is here, and I believe you 

 and others could not then avoid the true conclu- 

 sions as to the value of the solar constant. Un- 

 fortunately, owing to the unequal transparency of 

 the earth's atmosphere for rays of different wave- 

 lengths, it is absolutely necessary to use spectrum- 

 energy analysis to measure the solar constant of 

 radiation, as Langley showed. We use a linear 

 bolometer to measure the intensity and changes of 

 intensity of all parts of the spectrum. We have 

 employed it at Washington, Bassour, Hump Moun- 

 tain, Mount Wilson, and Mount Whitney. In our 

 experiments the solar beam traversed paths of air 

 ranging from that where the sun was nearly ver- 

 tically overhead at Mount Whitney, to that with 

 the sun on the horizon at Mount Wilson. Anybody 

 interested can learn exactly how we worked by 

 studying our published papers, particularly Vol- 

 umes II. and III. of our Annals and our paper 

 ' ' New Evidences on the Intensity of Solar Radia- 

 tion Outside the Atmosphere," Smithsonian Mis- 

 cellaneous Collections, Vol. 65, No. 4. 



In all this work we treat the pyrheliometer as a 

 subsidiary instrument. Its sole use and purpose in 

 our investigations is to enable us to express the 

 readings of the bolometer in calories. 



As a result of spectro-bolometric investigations 

 over fifteen years of time, we have shown that the 

 solar constant is 1.93 calories, and the sun an ir- 

 regular variable star. Others, Clayton and Bauer 

 particularly, have shown how the solar variations 

 we have discovered affect terrestrial things. If our 

 results were wrong these correlations would not be 

 found. 



7. Not everybody has a spectro-bolometer. You 

 haven't any, for one. From a wealth of experi- 

 ence that nobody else in the world ever had in the 

 measurement of solar radiation, we have put out 

 some tabular data and empirical formulse connect- 

 ing pyrheliometry and psychrometry with the solar 

 constant. We did this, not because we had any 

 occasion for them ourselves, but so that observers 



