152 CARNEGIE INSTITUTION 



corder, you can read every day the area of the resulting cur\'e. I 

 enclose you some sample records. Those marked A are taken with 

 the old receiver and B with the new one. You will see that in B 

 when there is no sunshine the curve falls to the zero line. In A it 

 is alwaj'S above it. 



I wish 5^ou could also see your way to carry on a series of obser- 

 vations by allowing an image of the sun to transit over the aperture 

 of a small radiomicrometer and recording the deflection on a moving 

 photographic plate. By a discussion of the resulting curves I think 

 it would be quite possible to determine whether the depth of the 

 absorbing layer on the sun varies during a sun spot cycle. I began 

 taking curves here, but the weather was so hopelessly unfavorable 

 that I gave it up. 



[^Froni Sir Norman Lockyer, Solar Physics Observatory, South Ken- 

 sington, Londo7i.'\ 



February 25, 1903. 

 In response to your letter of January 29 regarding the work to be 

 done by a new astrophysical observatory-, I would say that your 

 scheme practically covers the whole ground. There are, however, 

 one or two points to which attention might be drawn : 



1. Would it be advisable to erect a permanent building on a 

 mountain summit without first putting up a temporary building and 

 making observations from it for a j'ear or two ? 



2. It is of great importance that the observatory should not be 

 too far away from some large town easy of access, as modern work 

 requires the investigator to be in touch and personal contact with 

 scientific men for purposes of mutual assistance and advice in addi- 

 tion to the reasons given in your letter. 



3. It is important that the laboratory equipment should be com- 

 plete, for it is the mutual work of the observ^atory and the laboratory 

 which helps the investigation. 



4. The Janssen-Hale-Deslandres method of photographing the 

 solar prominences should undoubtedly be undertaken and made 

 strict routine work. 



I am very glad to see that you mention the photographing of the 

 ultra-violet end of stellar spectra, as this is important and we are at 

 work upon it, although we have very small means here for carrying 

 it on. 



