164 CARNEGIK 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 obsen^ations 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. 



\_From Professor Kjiut A?igstrdj?i, Royal University, Upsala, Sweden.^ 



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 pj'rheliometer 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 

 lyangley. 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 



