102 



This paper contains an account of the observatory, and of the 

 transit and magnetic declination instruments with which it was pro- 

 vided, of the mode and times of observing, with deductions from the 

 observations, and tables of the observations themselves. Among 

 other interesting matter, is the investigation of an empirical formula, 

 expressing the daily changes of magnetic declination in terms of the 

 solar time, by Prof. Peirce, and a comparison of the magnetic decli- 

 nation and dip deduced from Gauss' formula, with those elements as 

 obtained by observation. Besides the monthly term-days, several 

 extra days in each month had been devoted to observations at short 

 periods. The bi-hourly observations had not been attempted. The 

 paper closes with an account of the new observatory, and of the com- 

 plete set of magnetic instruments with which it is furnished. 



Dr. Hays invited the attention of the Society to a very ex- 

 tensive and highly interesting collection of fossil bones, chiefly 

 of the Mastodon, recently brought to this city by Mr. Albert 

 Koch, of St. Louis. 



Dr. H. stated that this collection comprises portions of twenty- 

 three lower and eleven upper jaws, of upwards of two hundred teeth, 

 and a sufficient number of the other bones to form a nearly complete 

 skeleton. 



Four of the lower jaws appertain to the genus Tetracaulodon. 

 One of these is remarkable from having a single alveolus for a tusk. 

 This alveolus is on the right side; and in its form, position, and size, 

 is similar to that of a specimen in the collection of the Society, de- 

 scribed and figured in the Transactions, Vol. IV. PI. XXIX. There 

 is not the slightest trace of a corresponding alveolus ever having ex- 

 isted on the other side. Two other jaws have also only a single al- 

 veolus ; but the specimens are too imperfect to determine whether or 

 not they had another, though Dr. H. infers that they had, and that 

 the existence of a single tusk in the lower jaw was a merely acci- 

 dental occurrence. The specimen described by Dr. Godman has 

 two, and also that belonging to the Museum of the University of Vir- 

 ginia. See Vol. IV. of the Transactions, Plates XXVI. and XXVII. 



The fragment of a fourth jaw is particularly interesting, from its 

 apparently belonging to a distinct variety, if not even a new species, 

 of Tetracaulodon. This consists of the chin, and a portion of the left 

 side. In the chin there is a small alveolus on each side. This jaw 

 is strikingly similar to one in the Cabinet of the Society, and described 



