62 PROCEEDINGS OF THE [Dec, 1868. 



the comer of Kiitledge, growing on the brick foundation of a wooden house, 

 on the South side of the street. This brick foundation rises about a foot above 

 the brick sidewalk of the street, is damp, aad occupied by Beboulea liemisplie- 

 rica, and sunilar Hepatics and Mosses, whicbdehght in such damp and shaded 

 situations. Among these the Fern is growing freely, and it is like none 

 of those known to inhabit this State. Its Qrigin, and the time of its introduc- 

 tion are unknown. 



A letter of resignation from Hon. Wm. Aiken was read and ac- 

 cepted. 



Prof. McCrady read a continuation of his paper on " The Law 

 of Development." * 



The following paper was read : 



ON THE OCCULTATOR. 



BY PKOF. LEWIS E. GIBBES. 



In the years 184:8-1854, I- was much engaged in observing occultations of 

 fixed stars by the moon, and as a means of obtaining the approximate times of 

 disappearance and reappearance with less labor than by calculation, I devised 

 and constructed, in 1849 or 1850, an inscrument for that purpose, to which I 

 gave no special name. This instrument is still in my possession, but not in use, 

 as certain parts, presently to be mentioned, have deteriorated with the lapse of 

 time. 



The Eev. Thomas Hill, of Cambridge, Mass. , has published in the Nov. num- 

 ber of Silliman's Journal, a description and figure of an instrument for the 

 same purpose, invented by him in 1842, and called by him the Occultator. As 

 the two mstruments have the same end in view, there is a general agreement in 

 plan, but the details differ. Mine is founded on the well known method of or- 

 thographic projection usually adopted m projecting eclipses and occultations, 

 and 1 have pubhshed no description of it, nor do i propose doing so at the 

 present time ; but I wish to mention now, the devices 1 adopted to overcome 

 certain difficulties which present themselves in both instruments, and the fol- 

 lowing explanations will be sutficiently intelhgible, without a figure, to those 

 familiar with the subject. 



Mr. Hill finds the desired projection, on the plane of the instrument, of any 

 point above that plane, as the extremity of a steel rod, by means of a silk thread 

 stretched on a brass bow, set on a triangular base, and made normal to the 

 chart or plane oi the instrument, by screws in the base. I effect the same end 



See Note page 61. 



