RUMFORD SPECTROHKLIOGRAPH. 148 



fotiiul on a liigli-Ievcl Iv^, pliolooraj)!!, I)iil it <li(l not appear on a K^ 

 j)hotograpli. This was confirmed by otlicr cxposiuvs. 



The results given by this first photogi-aph have been boi'ue out in 

 subsecpient work. It is found that the hyih-ogen flocculi are in gen- 

 eral dai'k. though they are sonietinies bright in disturbed regions, 

 usually m the neighborhood of sun spots." 



CONCLUl)IX(i KKMAKIvS. 



In concluding, we may perhaps be j)ei-niitted to speak of a few of 

 the numerous investigations which can be undertaken by the student 

 of solar physics. If proper use is to be made of the numerous meth- 

 ods of research which are now available, a large number of investiga- 

 tors will be needed, working, if, possible, on some cooperative plan, 

 at many stations Avidely separated in longitude. Even the adequate 

 use of the spectroheliograph alone Avould be beyond the capacity of 

 any single institution, for when suitably designed this instrument will 

 furnish as many photographs of the sun as there are elements present 

 in its atmosphere, and in addition to these many others which repre- 

 sent the peculiarities of certain lines. For example, we have already 

 seen that it will be desirable to ascertain in what degree photographs 

 taken with enhanced lines differ from those taken with other lines of 

 the same element. ^Vith a large image of the sun important results 

 might be expected to follow from a study of photographs of sun spots 

 taken with the aid of the widened lines and with bright lines or other 

 lines which are peculiar to the spot. In vicAv of the constant changes 

 which are going on in the sun, a' few photographs made in any of 

 these ways will not suffice. What is Avanted are series continued 

 through at least one sun-spot period, in order to discover the law^s 

 which govern the intensity and the distribution of the various gases 

 and metallic vapors. Furthermore, the great importance of eruptive 

 phenomena, their comparative rarity, and the brief time in which all 

 their i^hases are exhibited, call for special preparations and methods 

 of work. Spectr()heliogra[)hs capable of taking several photographs 

 at once through ditl'erent lines will be essential for an}^ suitable study 

 of eruptive phenomena. If a chain of observatories Avell distributed 

 in longitude could arrange their Avork so as to keep the sun almost 

 constantly under observation, many important eruptions Avliich are 

 now lost would be recorded. 



But it is by no means sufficient merely to take photographs of the 

 sun with the spectroheliogi-aph. In order to extend greatly the range 

 of the attack, and also to explain the spectroheliograph n^sults, 



" Many additional interesting details and conclusions regarding^ both calcium 

 and hydrogen fiocfuli are given in the original paper and should be consulted 

 by -the special reader. 



