REPORT OF THE SECRETARY. 19 



In summer the curve appeara to have but one greatest and one 

 least ordinate occurring about noon and midnight. In winter the 

 double feature of the curve becomes quite conspicuous. 



The vertical force appears greater in May, June, July, and August, 

 and less in the remaining months, with a range of about a hundred 

 md five hundred thousandth part of the whole force. 



The ninth part gives the investigation of the influence of the moon 

 upon the vertical force ; also upon the direction and intensity of the 

 total force. The methods of investigation are the same in this as in 

 the preceding parts. The daily effects of the moon exhibit a prin- 

 cipal maximum a little before the planet passes the upper meridian, 

 and a principal minimum about three hours after it passes the lower 

 meridian. The average epoch of the tide of vertical force is about 

 one and a half hour in advance, apparently, of the culmination of the 

 moon. A secondary variation of this force, though noticed, is very 

 feeble. The subject of the time of greatest lunar disturbance is yet 

 very imperfectly developed, and more observations in regard to it 

 are desirable. 



A comparison is also given in this paper between the observations 

 made at Toronto and Philadelphia, and their accordances or differ- 

 ences are stated. The effect of the moon upon the direction and inten- 

 sity of the total force is obtained by a combination of the vertical 

 and horizontal components. From this part of the investigation it 

 appears that the dip is greatest at 8 and 20 hours, and least at 3 

 hours and 13.\, the range being equal to 3.6 seconds ; and ako that 

 the maximum strength of the earth is greatest at half-past 12 and 11, 

 and least at 7^ and IT hours, the results, from the observations at 

 Toronto and Philadelphia, being remarkably coincident. 



The next paper of the foregoing list is that by Dr. Dean, which 

 comprises the anatomy of the medulla oblongata, both human and 

 comparative; from the lowest roots of the hypoglossal nerve, through 

 the upper roots of the auditory, including the hypoglossal, nasal, 

 glossopharyngeal, abducens, facial, and auditory nerves. The ob- 

 jects of the investigation were principally as follows : 



1st. To illustrate the topography of the medulla oblongata by means 

 of a series of photographs, which might completely map out all the 

 principal changes in structure as they successively occur, connected 

 with the development of the different nerves, with the details which 

 accompany the development of their nuclei and accessory ganglia. 



2d. The study of the more minute histological, details, such as the 

 course of the nerve roots, their entrance into their respective nuclei 



