1883.] Circular concerning Astronomical Photography. 261 



parts of an historical series. Where photography is regularly em- 

 ployed in a continuous series of observations, it is obvious that 

 specimen negatives only can be spared for a collection. But in such 

 cases it is hoped that some duplicates may be available, and that 

 occasional negatives may hereafter be taken for the purpose of being 

 added to the collection, to exhibit recent improvements or striking 

 phenomena. 



When negatives cannot be furnished, glass positives, taken if 

 possible by direct printing, would b© very useful. If these also are 

 not procurable, photographic prints - or engravings would be desir- 

 able. 



In connexion with the photographs themselves, copies of memoirs or 

 communications relating to the specimens sent, or to the general subject 

 of astronomical photography, would form an interesting supplement to 

 the collection. A part of the contemplated scheme will involve the 

 preparation of a complete bibliography of the subject, including a list 

 of unpublished photographs not hitherto mentioned in works to which 

 reference may be made. 



The expense which may be incurred by contributors to the collec- 

 tion in the preparation and transmission of specimens will be gladly 

 repaid by the Harvard College Observatory when desired. 



EDWARD C. PICKERING, 

 Director of the Harvard College Observatory . 



Cambridge, Mass., 



February 21, 1883. 



