116 MODES OF MEASURING MINUTE INTERVALS OF TIME. 
so sensible that it received a legible impression from a printed surface during the flash of 
an electric spark. This should give sensibility enough for the concentrated light of a star 
from a large object glass. By having, therefore, a surface of this kind moving with a de- 
fined velocity transversely to the direction of the star’s path transiting the field of view, 
we should obtain the recorded signals, which we want. The requisite arrangements for 
such an effect, with reference to the eye piece and the transit wires, are sufficiently obvi- 
ous. Determinate distances along the prepared sensitive surface in the direction of its 
motion would mark the times. The star’s motion would be indicated by a dark line 
crossing this surface. If the transit wires were illuminated, they would appear on the 
surface as dark lines, parallel to the direction of its motion. The line of the star’s motion 
would cross these obliquely, at an angle determined by the velocity of movement given to 
the surface. The effect of inflection at the edges of the transit wires, and of imperfection 
of focus in the instrument, might render these lines somewhat broad and indistinct as to 
their lateral boundaries; but points of coincidence in their axes would probably be deter- 
minable, with considerable precision. If the transit wires were not illuminated, they 
would then produce an interruption, or a difference of shade, in the line of the star’s path, 
which might serve perhaps better to mark the instants of contact. A suitable degree of 
artistic skill may make lines on the prepared surface itself to become substitutes for the 
transit wires. With the employment of a good object glass alone, and with means of di- 
recting its line of collimation, in combination with arrangements of the sort now alluded 
to, it does not appear difficult to substitute the astronomical clock or chronometer, for the 
living observer, and to reduce almost indefinitely the causes of uncertainty in respect to 
siderial astronomy. To apply the same principle to the movements of the sun and moon 
would require some farther modifications, but most inquiries with regard to the movements 
of the planets and of conspicuous or solitary stars, would be facilitated and rendered more 
precise if these suggestions can be carried out. 
