314 ANNUAL OF SCIENTIFIC DISCOVERY. 



ments and apparatus, and by the gift of books, as well as by im- 

 portant and valuable suggestions. Four assistants will accompany 

 me, Messrs. Miles Rock, John M. Thome, Clarence L. Hath- 

 away, and William M. Davis, Jr. We hope to reach Buenos 

 Ayres not later than the middle of August. The building is now 

 under construction in Boston. The means available proved inade- 

 quate for its construction according to the original plan, which was 

 in the form of a cross, with 4 square rooms about its centre, and tur- 

 rets at its 4 extremities. One-half of it will be first erected, and 

 it is hoped that the remaining portion will speedily be added." 

 Nature. 



ARTIFICIAL HORIZON. 



At the Troy meeting of the American Association, Mr. Hilgard 

 exhibited a very ingenious arrangement of J. H. Lane, by which 

 the vibration or ripple, which acts so annoyingly under many cir- 

 cumstances with the ordinary tank of mercury, is effectively sup- 

 pressed. 



It consists of a shallow dish, with a circular groove around its 

 edge, and a cavity beneath, which communicates with the groove 

 by a space, while by means of a tube air may be blown at will 

 into the cavity. This cavity and the circular groove are filled 

 with mercury. By blowing into the cavity, more mercury is 

 raised and overflows into the central portion of the dish. On now 

 allowing the air to escape and the excess of mercury to flow back 

 into the cavity, a film, held by its. cohesive force, is retained over 

 the surface, and, by reason of its thinness, this is incapable of 

 maintaining a vibratory or ripple movement. A touch with the 

 finger will instantly break up this surface ; but it is easily re- 

 formed, and experience has shown that it is not deflected from its 

 horizontal direction by slight inclination of the dish. 



THE NEW CAMBRIDGE TRANSIT INSTRUMENT. 



During a late visit to Cambridge, we had the pleasure of ex- 

 amining the above-named piece of apparatus, which has just been 

 added to the appliances of this observatory, and which contains 

 many novelties of construction and arrangement (due to the in- 

 vention of Professor Winlock) worthy of special notice, and with- 

 out doubt generally interesting to our readers. 



In the first place, with reference to its mounting. 



The pivots are not supported in Y's, but on account of the great 

 weight of the instrument, as well as for other reasons developed 

 by experience, have journals accurately fitted to them. These 

 journals, in their turn, are not provided with means of adjust- 

 ment, but are permanently attached to plates set in the piers, and 

 brought, by scraping and repeated trials, to the exact surface re- 

 quired for an accurate adjustment of the instrument once for all. 



Another novelty consists in the arrangement of the setting 

 levels and circles at the eye end, which are turned by a gear 

 wheel, in place of the clamp and tangent screw, which is so apt to 



