RUMFORI) SPECTROHELIOGEAPH. 135 



this telescope, would soon be ready for use. But the funds refjuired 

 for the construction of -the new spectroheliograph were not forth- 

 coming, and when it finally became possible to undertake w-ork on 

 this instrument (through a grant from the Kumford fund, and the 

 gifts of friends of the oliservatory) progress was slow, owing to the 

 limited funds available. For a 7-inch solar image, collimator and 

 camera lenses of about 10 inches (25.4 cm.) aperture were needed; 

 but the considerable cost of such lenses rendered their purchase 

 impossible, and a pair of Bi-inch (15.T cm.) Voigtliinder portrait 

 lenses, obtained from second-hand dealers after a year's search, were 

 adopted. With lenses of this aperture it is evident that much light 

 must be lost at the extremities of the slit, and that the resulting image 

 of the sun must therefore be deficient in brightness at the correspond- 

 ing liml)s. Even after the lenses had been secured, the demands of 

 other i^hases of the observatory's work greatly retarded the construc- 

 tion of the instrument, and it was not until the latter ])art of l.S*)l) 

 that it was ready for trial." * * 



prem:\mxary account or results obtained with the rumford 



SPECTROIIELIOORAPII. 



Prior to r,)0:'> the Rumford spei'troheliograph was used for experi- 

 mental pui-poscs, the numerous photographs ol)tained during the sun- 

 spot minimum being of service mainly in perfecting the adjustments 

 of the instrument. It had been exi)ected that the spectroheliogra])h 

 would be transfered from the 40-incli refractor to the 30-inch ccelostat 

 reflector for the purposes of the daily record; but the destruction of 

 the latter instrument by fire in December, 1902, prevented the reali- 

 zation of this i)l:in.'' The work with the 40 inch refractor was accord- 

 ingly resumed in February, 1903, and since the latter part of that 

 month photograi)hs of the calcium flocculi have been made on each 

 clear day (Sundays usually excepted). Since early in April this 

 series has been supplemented by a daily series of (low-level) photo- 

 graphs, made with the slit set at some distance from the center of the 

 II or K band, and since May IC photographs have been made as often 

 as possible witli the H/i line. In addition to this routine work many 

 photogra])hs of special regions have been taken in a study of the 

 calcium vapor at various levels, and some results have also been 

 obtained with the calcium line A 4,-2-20.i), the iron line A 4,383.7, and 

 with various other dark lines. It will thus be seen that while the 

 material represented by the photographs obtained with the Rumford 



"There follows a description of the Ruiuford siJectroheliograph, foi- which the 

 reader may consult the original imhlicntion. 



b^Mirongh the generosity of -Miss Helen Snow the (-(eldstat retii'ctor has l)een 

 relmilt and is now in regular use. A spectreheliitgrai)h will soon l)e employed 

 with it. 



