Review of Dr. Jackson’s Final Report, &c. 27 
fined by a nut, and turns with some friction. Thirty six holes, 
half an inch in diameter, are bored through the ring, having their 
centres carefully arranged in a circumference concentric with the 
axis. Another hole of the same size is made near the top of the 
pillar, with which each one in the ring comes in range, as it is 
turned. The plates of punctured lead, and other inflecting ob- 
jects, are placed upon the apertures in the ring, being let into the 
surface of the wood by shallow dove-tailed recesses, or fastened 
in any other convenient way. A light spring (e) falls into a 
notch in the edge of the ring, whenever the aperture of the pillar 
coincides with one of those in the ring, as the latter is turned on 
its axis. The hole in the pillar being once adjusted in the line 
with the magnifier and the focus of light, the ring may be turned 
as fast as the experimenter chooses; and the inflecting patterns 
will all come in succession to the proper place to be seen by the 
observer. The. spring offers a slight check to the motion, as 
often as an aperture of the ring attains the right position. 
The instrument here described is already furnished with about 
thirty varieties of inflecting objects. A large proportion of them 
are made of sheet lead, with punctures and slits variously com- 
bined. Other holes are occupied respectively with a net of fine 
Wire, a piece of fine comb, screws of delicate thread, placed 
almost in contact, &c. A very fine effect is produced by two 
pieces of fine ivory comb, one fastened in the aperture and the 
other fixed in a revolving cap; the latter, as it is turned round, 
makes, in conjunction with the former, a net-work of all possible 
angles, while the picture seen through the magnifier every mo- 
ment changes its pattern and its color in the most Berets - 
wonderful manner. 
Arr. IIf.—Review of Dr. ©. 'T. Jacxson’s Final Report on the 
Geology and Mineralogy of the State of New Hampshire. 
(Read before the Boston Society of Natural History, by Tuomas T, Bouyé, 
; March 5th, 1845.) 
Tue survey of the State of New Hampshire was made under 
an act passed: by its legislature during the session of 1839. 
- In September of that year, Dr. Jackson received his commis- 
sion as State geologist, and he commenced his duties under it om 
