164 CARNEGIE INSTITUTION 



across the central meridian of Jupiter, revealing not a few interest- 

 ing relations ; but necessarily he will not be able to remain much 

 longer at that station, nor can he give to his observations the full 

 discussion they deserve. If work similar to his could be undertaken 

 by a professional astronomer, who would have the time to fully dis- 

 cuss his results, at a permanent observatory, which would secure 

 continuity to the work, I think it would ere long lead to our under- 

 standing the condition of Jupiter far better than we can at present. 

 Obviously an equatorial or at least a tropical site for such an observ- 

 atory would, as Captain Molesworth has found, have great ad- 

 vantages. 



Q 



[From Professor Knid Angstrom, Royal University , Upsala, Swcdcn.~\ 



May 16, 1903. 



I beg you to excuse my long delay in answering your very inter- 

 esting communication on the astrophysical observatory planned by 

 the Carnegie Institution, but a great many duties have hitherto made 

 it impossible for me to reply. I hope, however, that you will not 

 see in that delay a proof of indifference regarding a question that in 

 fact interests me profoundly. 



Unfortunately I can give no information as to the site of the ob- 

 servatory, having no personal experience with regard to the atmos- 

 pheric conditions in the mountains of California. The establishment 

 of two corresponding observatories at different heights will certainly 

 be most valuable for the scientific results. As to the choice of a 

 place, it will probably be of great importance to study the local con- 

 ditions. My experience, derived from visits to Teneriffe, is that on 

 the northern side of the mountain it is almost impossible to get sat- 

 isfactory results in solar observations, while the southern side is very 

 favorable for that purpose. 



As to the instruments for measuring the total radiation of the sun, 

 I am sure that the compensation pyrheliometer is at present the only 

 convenient instrument, and I am willing to superintend the construc- 

 tion of the instruments that the observatory may think proper to 

 order from the mechanician Rose in Upsala. 



Probably the program of the observatory comprises also the regis- 

 tration of spectral energy by means of the instrument of Professor 

 Langley. I may, however, call your attention to the advantage of 

 making the registration also with another instrument, with less dis- 

 persion, which in a shorter time could give a general view of the 



