410 



SCIENCE. 



[N. S. Vol. XXI. No. 533. 



This is far from being true of key observa- 

 tions. 



The transit micrometer is about to be 

 put into use in the regular longitude work 

 of the Coast and Geodetic Survey. 



I predict, basing my prediction upon the 

 general experience with transit micrometers 

 as well as on these particular tests, that 

 with a transit micrometer three nights of 

 observations without an exchange of ob- 

 servers will give as great accuracy as has 

 been secured in the past from ten nights 

 of observations with a key, including an 

 exchange of observers. This is a predic- 

 tion of which the truth or falsity can only 

 be proved conclusively by field experience. 

 I rely upon such experience to be gained 

 within the next five years to verify the 

 prediction. 



I venture to predict also that the evi- 

 dence in favor of the transit micrometer 

 will accumulate to such an extent in the 

 next ten years in fixed observatories, as 

 well as with portable instruments, that the 

 astronomer who uses a key in 1914 for 

 accurate time determinations or determina- 

 tions of right ascension will have difficulty 

 in furnishing adequate explanation of his 

 conduct. 



An illustrated description of the Coast 

 and Geodetic Survey transit micrometer, 

 with a full report of the tests referred to 

 above, and a brief resume of a part of the 

 literature of the transit micrometer, is now 

 being printed as an appendix to the Coast 

 and Geodetic Survey Report for 1904. 



Remeasiirement of the Hough Double 



Stars: Eric Doolittle. 



The catalogues of new double stars pub- 

 lished by Professor Hough comprise 622 

 pairs, of which 77 are closer than ^" and 

 143 closer than 1"; in those pairs in which 

 the distance is greater than 5" the com- 

 panion is usually excessively faint ; in fact, 

 there are few of the stars which would not 



be difficult with a telescope of much less 

 than 18 inches apei'ture. 



The measurement of this fine series of 

 doubles seems to have been strangely 

 neglected. On a few of them, which are 

 of the type of close pairs of equal magni- 

 tude, as 98, 260 and 296, there are a num- 

 ber of rather discordant measures, but the 

 great majoritj^ have received no attention 

 except from the discoverer himself. Thus 

 there are but 87 pairs which have been 

 measured in two dift'erent years, and on 

 no Jess than 358 there is but a single prior 

 measure. 



The entire list was, therefore, added to 

 the observing list for the 18-inch refractor 

 of the Flower Observatory. Thus far, 360 

 pairs have been measured on three or more 

 nights and many of the remaining 262 are 

 partially measured: a single night's meas- 

 ure consists in each case of at least four 

 measures of position angle and four of the 

 double distance. 



Change has been found in 16 of the close 

 pairs, and among the wider ones there is in 

 33 instances indication of proper motion. 



It is the intention, when the work is com- 

 pleted, to publish a catalogue of these stars, 

 including about twenty new pairs which 

 Professor Hough has discovered since his 

 last list was issued. 



A Study of the Driving-worms of Several 

 Plwtographic Telescopes: Edward S. 

 King. 



In following a star with a photographic 

 telescope we must have for the period of 

 the exposure a clock the hour hand of 

 which will indicate the elapsed time on a 

 scale graduated to seconds or less. "We 

 must have the equivalent of being able to 

 determine the time by measuring the posi- 

 tion of the hour hand with a micrometer. 

 If any periodic error occurs in the train 

 of the driving mechanism, causing the tele- 

 scope to be first in advance of, and then 



