RITMFOTIT) SPErTTiOnKLTOflRArn. 135 



(his toloscopo. would soon he ready i'ov use. But the funds r(H|ui]-('d 

 for tlie conslrncl ion of the new siH'clroheliogriiph were not forth- 

 coniinii'. and when it (inally hecame possible to undertake w()i'i< on 

 this insti'ument ( through a orant from the Runiford fund, and the 

 •lifts of friends of the observatory) i)rogress 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; 

 hut the considerable cost of such lenses rendered their pui'chase 

 impossible, and a pair of 6] -inch (IT). 7 cm.) Yoigtliinder poi-trait 

 kMises. obtained fi-om second-hand dealers after a year's search, were 

 ado})ted. AVith lenses of this aperture^ it is evident that much light 

 unist 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 s(>cured, the demands of 

 other phases of the observatory's work greatly retarded the construc- 

 tion of the instrument, and it was not until the latter i)art of lSOi> 

 that it was ready for trial." * ^■ 



PRELIMIXARY ACCOUNT OF RESULTS OBTAINED WITH THE RUIMFORD 

 SPECTROHELIOGRAPir. 



Prior to 11»();> the Rumford spectroheliograph was used for experi- 

 mental purposes, the numerous photographs obtained during the sun- 

 spot mininnun being of service mainly in perfecting the adjustments 

 of the instrument. It had been expected that the spectroheliograph 

 would l)e transfered from the 40-incli refractor to the 80-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 plan.'' The work with the -tO-inch refractor was accord- 

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

 month photographs of the calcium flocculi have been made 6n each 

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

 series has been supjjlemented 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 1() photographs have been nnule as often 

 as possible with the H/^line. In addition to this routine work many 

 photographs of special regions have been taken in a study of the 

 calcium vapor at \arious levels, and some results have also been 

 obtained with the calcium line A 4,22().9, the iron line >V 4,883.7, and 

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

 material represented by the photographs obtained with the Rumford 



o There follows a tloscription of the Ruiufonl sitoctroliolioiLirapli. 1"<>1' which the 

 reader may consult the original publication. 



'' 'rhrough the generosity of iNIiss Helen Snow the coelostat reflector has been 

 rebuilt aiul is now in regular use. A spectroheliograph will soon be euiploj'ed 

 with it. 



