38 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



circle reads to 2" for locating it. The telescope is provided 

 with a position micrometer by the Chirks, and a double-image 

 micrometer by Browning, of London, for the purpose of exact 

 measurements. There are two spectroscopes by Browning 

 and Grunow. The observers are Mr. Seagrave and Mr. L. 

 Waldo, of Harvard College Observatory. From an account 

 of the observatory it is learned that the observers contem- 

 plate prosecuting two plans of work. "One of these re- 

 searches is the measurement of such of the close double stars 

 discovered by our distinguished fellow-countryman S. W. 

 Burnham, Esq., of Chicago, as we can reach with our optical 

 mea*ns. The second research is the continuous and exhaust- 

 ive measurement of one or two stars which have shown unu- 

 sually large annual motions in the heavens, to determine, if 

 possible, their parallax." 



In the list of papers read to the Scientific Association of 

 the Johns-Hopkins University, and as yet unpublished, the 

 only one relating to astronomy is by Dr. C. S. Hastings, " On 

 a True Criterion for Color-Correction in the Astronomical Ob- 

 jective." The formula) arrived at have been put to a practical 

 test by Dr. Hastings in the making of a 4-inch object-glass. 



A commission appointed by the French Chamber of Dep- 

 uties has reported favorably on the erection of a larsre ob- 

 servatory at Meudon. The credit given is 690,000 francs 

 (^138,000), of which $78,000 are for the purchase of a large 

 refractor. M. Janssen will be, as before, the director. 



Mr. Lockyer has published in Nature a series of articles 

 on the "Modern Telescope," which gives a useful and con- 

 venient popular summary of the principal defects and advan- 

 tages of the telescopes now in use. The paper by Mr. Grubb 

 on the same subject is taken as a basis, and some of the dif- 

 ficulties described by Mr. Grubb are considered. 



Mr. Henry Bessemer, in considering these difficulties, has 

 been led to propose (Nature, January 24, 1878) a plan for 

 overcoming the difficulties in mounting and figuring laro-e 

 glass reflectors, according to which plan he is now making a 

 50-J-inch silvered glass reflector. First, as to support : a rib- 

 bed casting of iron 52. V inches in diameter and 13 inches thick, 

 weighing 1400 pounds, is to be made and annealed in oil. Its 

 face will be turned to a true plane, and a spiral groove one 

 sixteenth of an inch deep and wide will be cut all over this 



