378 Proceedings of Scientific Societies. 



Dr. Horner alludes to the erroneous nature of the early ideas of natu- 

 ralists on the teeth of the mastodon, and observes that we now know, with 

 some degree of certainty, that the earliest teeth of this animal were not 

 more than an inch and a half square, and that the three immediately suc- 

 ceeding were a gradual and successive enlargement on this and on each 

 other's volume. In the museum of Mr. Koch, at St. Louis, there is a 

 young head, the long diameter of which is IS or 20 inches, where the fact 

 of four co-existent teeth on each side of each jaw is exhibited. This spe- 

 cimen, with a dozen lower jaws of different ages and sizes, enables us to 

 trace, with some accuracy, the stages of dentition, until it reaches the 

 large and solitary grinder of ten inches in length on each side. Judging 

 from these phases of dentition. Dr. Horner infers that the entire amount 

 of teeth was at least 24 ; he is disposed, indeed, to think that the number 

 may have been greater than this ; perhaps 28, and possibly 32. 



Dr. Horner makes some observations on some specimens of lower jaws 

 in Mr. Koch's museum in St. Louis, in which there was a solitary tusk on 

 the right side, and alludes to the embarrassments that their existence oc- 

 casions in regard to the Tetracaulodon of Godman ; whether, for example, 

 we are to consider them merely as abnormous types of that animal, as 

 known mastodons, or as still another species to which, if such, the name 

 Tetracaulodon might be attached. Dr. Horner confesses himself unable 

 to suggest a probable solution of these questions, and states, in connection 

 with them, that Mr. Koch has the lower part of the head of a mastodon of 

 middling size, in which, from the intermaxillary bone, as usual, protrudes 

 a tusk, which measures thirty inches long by four inches in diameter ; but 

 the tusk exists only on the left side, there being not even a vestige of alve- 

 olus on the right. 



It is very far from being certain. Dr. Horner adds, that any example 

 exists of the upper jaw of the Tetracaulodon ; the presence of tusks in both 

 jaws at once has therefore to be yet proved. 



The committee consisting of Prof. Bache, Dr. Patterson, and Mr. Lu- 

 kens, to whom was referred the paper, entitled "observations to deter- 

 mine the magnetic intensity at several places in the United States, with 

 some additional observations of the magnetic dip, by Elias Loomis, pro- 

 fessor of mathematics and natural philosophy in Western Reserve Col- 

 lege," recommended the same for publication in the Society's Transac- 

 tions, which was ordered accordingly. 



The following is an abstract of the results of observations contained in 

 this memoir. 



1. Magnetic Intensity. — The horizontal intensity was observed by an 

 apparatus similar to the one used by Prof. Hansteen. Three small nee- 

 dles furnished to the author by Prof Renwick, and made under the direc- 

 tion, respectively, of Professor Hansteen, Major Sabine, and Prof Henry, 

 were employed. The commencing serai-arc of vibration was, in every 



