116 RECORD OF SCIENCE FOR 1886. 



Stellar pliotograpliy at Harvard College Observatory. — Professor Pick- 

 ering's iuvestigatiotis, which were briefly referred to in last year's re- 

 port, have been i^ublished in full iu the ]\Iemoirs of tlie xVmerican 

 Academy (vol. 11, pp- 179-22G). His paper contains a sketch of the 

 history of the subject, description of the apparatus, discussion of 

 theoretical considerations, and some results obtained in the three depart- 

 ments of "star-charting, photographing star trails, and spectrum pho- 

 tography." His work on the jjhotography of stellar spectra we have 

 already alluded to in the present review. 



In the report of the Harvard Observatory for 1886 it is stated that 

 the investigation in stellar photography undertaken with the aid of 

 the Bache fund is now nearly completed. The principal results ob- 

 tained include photographs of the entire sky north of — 30°, on which 

 all stars bright enough to leave trails without the aid of clock-work are 

 depicted. One series of plates exhibits the effect of atmospheric ab- 

 sorption on nearly every night of observation for a year 5 and among the 

 miscellaneous observations may be mentioned some experiments in the 

 application of photography to transit instruments, which showed that 

 the accidental errors did not reach one-half of those affecting eye- 

 observations. Various pliotographs were taken of the nebula of Orion 

 to show the relative brightness of different portions of this object. 

 The nebulae in Andromeda, in Lyra, and in the Pleiades were also 

 photographed. An attempt was made to photograph a satellite of 

 Jupiter while undergoing eclipse, and thus to determine the time of this 

 phenomenon. 



Astronomical photography at the LicJc Observatory. — In a very interest- 

 ing article upon astronomical photography, published in the Overland 

 Monthly for Ii^Tovember, 188G, Professor Holden thus summarizes the 

 facilities of the California observatory for investigations in this field: 

 "We expect to have a photographic objective as large as 36 inches in 

 aperture, if the glass for this can be obtained. This will be mounted 

 in the most perfect manner, and we shall emjiloy the 12-iuch Clark 

 telescope, now at the observatory, as a pointing telescope for the large 

 objective. The 12-inch telescope will be mounted alongside the other. 

 An electrically-controlled driving clock will keep the two telescopes 

 accurately directed during the exposure. Our objective will collect nine 

 times the light of any other photographic telescope now made. - - - 

 The focal length of the combination will be about 580 inches, and 1" on 

 the plate will therefore be 0.002 inch. This is a quantity whose -^q part 

 can easily be measured. A single exposure will give us a map of the 

 sky con»prising four square degrees on a plate 21 by 24 inches. - - • - 

 The sun's image unmagnified will be 6 inches in diameter ; a large sun- 

 spot will be the size of one's finger-nail. - - - The photographs of 

 the moon in the focus of the Lick equatorial will be 6 inches in diam- 

 eter, and will probably stand an enlargement of twelve times, so as to 

 be 6 feet finally." 



