164 Proceedings of the British Association. 
object of the machine is to apply to the numerical calculation of 
definite integrals, a principle first suggested by M. Poncelet for 
the registration of dynamometrical admeasurements, which has 
been applied by M. Morin to an instrument called the Compteur, 
for registering the traction of loaded carriages upon common 
roads, and during the last year, by a committee of the Associa- 
tion, to a permanent registration of the work of the steam upon 
the piston of a steam engine. 
On determining distances by the aid of the Telescope, by 
Mr. Bowman. The principle of this method was to observe the 
number of divisions of a graduated staff placed at a distance ; 
and considerable ingenuity is shown in determining the distance 
by making the necessary corrections on this observed number. 
The author thinks his method would be more accurate in sur- 
veying than the actual measurement by the chain, particularly 
in uneven ground; and asserts that the error in taking any dis- 
tance could not exceed the thousandth part of the entire distance ; 
hence, by dividing the entire distance, even when large, intoa 
number of parts, he conceives that great precision would be at- 
tained. 
Sir J. Herschel transmitted fifteen specimens of jer photo- 
graphic copies of engravings and mezzotintos, into the prepara- 
tion of which no metallic ingredient enters, the whole being 
tinted with substances of vegetable origin variously prepared. 
The rays of the spectrum which have eaten away the lights in 
these photographs, are neither the so-called chemical rays beyond 
the violet, nor the calorific rays beyond the red. The actiomis 
confined ree entirely to the luminous rays, and of these more 
cially to. those rays of the spectrum whose union forms @ 
color supplementary to that of the ground-tint; a circumstance, 
which, considering the great command of color which this new 
variety of the photographic art affords, holds out no slight hope 
of a solution of the problem of a photographic se iatareeneeit a 
natural objects in their proper colors, 
(To be concluded in the next number.) 
