Rev. W. Hodgson’s Description of the Chronoscope. 27) 
tween their edges at one angle of the rhomb, the number of 
transits is increased from one to four or even five; thus af- 
fording five pairs of observations for altitudes, or, counting 
first and last contacts, as many as twenty observations in 
all. 
If the axes, about which the instrument is moveable, are 
fitted with graduated circles and verniers, it becomes capable 
of measuring angles in a vertical, horizontal, or any other 
plane, between any objects which are sufficiently bright to be 
seen after three reflections: or if the rhomb is fitted perpen- 
dicularly upon the circumference of a graduated circle, which 
is moveable in a plane parallel to the equator, it becomes an 
accurate solar clock, which will give the true apparent time at 
any hour when the sun is visible. 
The principles employed are similar to, but not identical 
with, those of several well-known instruments. In the ordi- 
nary way of using the sextant or reflecting circle, the incli- 
nation of the planes passing through two objects is found by 
bringing one of the objects, seen without any reflection, to 
coincide with an image of the other produced by two reflec- 
tions. When these instruments are used with the artificial 
horizon for measuring altitudes, in the one case, the unre- 
flected object is brought to coincide with an image of the 
other produced by ¢hree reflections; and in the other case, 
_ “the plane in which the body is, is determined by three re- 
 flecting planes combined” in a manner “ whereby they are 
used as one single and double reflector.’ The principle thus 
last stated, has been very ingeniously employed by the inven- 
_ tor of the dipleidescope, but it is obvious that, before the pro- 
_ duction of that instrument, the principle itself had been in al- 
- most constant use. In order, however, to effect the end aimed 
at by the dipleidescope or by the sextant and artificial horizon, 
it is not necessary to restrict the comparison to the two cases 
of (1.) the object and the trebly-reflected image ; and (2.), the 
singly and doubly reflected images: for the same purpose is an- 
swered by bringing into coincidence with the object, or with 
its image produced by 2, 4, 6, &c., 2 », reflections, any of its 
images produced by 1, 3, 5, 7, &e., 2 + 1 reflections. In 
