200 SCIENTIFIC RECORD FOR 1884. 



evenings in September, used a power of ],000 and even of 1,500, and 

 perceived the fine details of planetary disks with admirable sharpness. 

 Tlie imajies of bright stars were of perfect regularity, and the central 

 part of the diffraction disk was so remarkably small that it may be ex- 

 pected that the instrument would also be very suited for observing 

 double stars.'' 



The almucantar. — This is the name given by Mr. S. C. Chandler, of 

 Harvard College Observatory, to an ingenious instrument devised by 

 him. It consists first of a rectangular basin filled with mercury. In 

 this mercury is floated a rectangle of metal, which carries a telescope 

 movable in altitude. The mercury basin can be moved in a horizontal 

 plane. The vertical transits of stars can be observed over horizontal 

 threads in the telescope. Such results as have been published show 

 the work of this instrument to be of surprising accuracy, and it cer- 

 tainly presents some important theoretical advantages. 



Dr. A. Steiuheil has given (Ast, Nach. 260G) in a brief form, a paper 

 on the errors and adjustments of object glasses of two lenses, which 

 should be studied by all observers who desire to understand the opera- 

 tion of their telescopes. An abstract of this has been printed in the 

 Sidereal Messenger. Dr. Steiuheil is prepared to furnish sets of objec- 

 tivcs each of which has o/^e of the errors named, but is perfect as re- 

 spcitts the remaining ones. These should be of value in our physical 

 la! -.or. 1 lories. 



lui'okTs position-micrometer. — The price of a Eepsold micrometer like 

 that described in the Encyclopcedia Britanica., vol. xvi — article micro- 

 meter—for a 15-inch telescope, is $1,250. This includes, of course, the 

 fittings to the telescope which give the bright wire illumination. 



Normal clock. — Dr. L. Waldo, Science states, has just completed the 

 erection of a normal clock at the Yale College Observatory, to be used as 

 a mean-time standard in the horological work of that institution. The 

 movement and pendulum are parts of the gravity escapement clock 

 built by Kichard Bond (Xo. 367), and which had a phenomenal record 

 under Mr. Rartnup, at Liverpool, and later under Prof. W. A. Eogers, 

 of Cambridge. The case, from Dr. Waldo's designs, is built of cast 

 iron, with planed back and front, to which are clamped the plate-glass 

 doors. The entire case rests upon two brick piers, which rise to the 

 height of the movement, and insure stability to the pendulum suspen- 

 sion. Thermometers, a barometer, and a cup of calcic chloride are 

 placed within the case, which can be exhausted to any barometric press- 

 ure desired by an air pump attached to its side. The escapement and 

 arc of vibration can be observed and adjusted with the greatest accu- 

 racy. The clock is erected in the clock-room of the observatory, which 

 was specially built to secure uniformity of temperature. 



Dirision errors. — Prof. W. A. Pogers has devised a means of deter- 

 mining the division errors of a meridian circle mechanically without re- 

 moving the circle from the axis. An abstract of his j)aper has appeared 



