before the. British Association. 311 
_ ceous: yet, though no method of fixing them has hitherto been 
_- discovered, we cannot doubt that the difficulty will be surmount- 
ed, and that we shall yet see all the colors of the natural world 
transferred by their own rays to surfaces both of silverand paper. 
_ But the most important fact in photography which I have now to 
_ Mention, is the singular-acceleration of the process discovered by 
- Niepce, which enables him to take the picture of a landscape 
illuminated by diffused light, in a single second, or at most in two 
seconds. By this process he obtained a picture of the sun on al- 
previously made by M. Arago, by means of a silver plate, that 
the rays which proceed from the.central’ parts of the sun’s disc 
have a higher photogenic. action than those which issue from its 
~ margin. This interesting discovery of M. Arago is one of a se- 
Ties on photometry which that distinguished philosopher is now 
* Civilized world will deplore—the loss of that sight which has de- 
_ tected. so many brilliant phenomena and penetrated so deeply 
ek 
ae 
ot into the mysteries of the material world, he is now completing, 
With the aid of other eyes than his own, those splendid research- 
glory of his country. 
_ From these brief notices of the progress of science I must now 
call yonr attention to two important objects with which the Brit- 
ish Association has been occupied since their last meeting. It 
has been long known both from theory and in practice, that the 
‘MMperfect transparency of the earth’s atmosphere, and the unequal 
retraction which arises from differences of temperature combine 
to set a limit to the use of high magnifying powers in our tele- 
~ Hitherto, however, the application of such high powers 
sco 
and it is only since the construction of Lord Rosse’s telescope that 
astronomers have found that, in our damp and variable climate, it 
_ 1s only during a few days of the year that telescopes of such mag 
- nitude can use successfully the high magnifying powers which they - 
are capable of bearing. Even ina-cloudless sky, when the stars are 
Sparkling in the firmament, the astronomer is baftled by influences 
Which are invisible; and while new planets and new satellites are 
being discovered by instruments comparatively small, the gigantic 
Polyphemus lies slumbering in his cave, blinded by thermal cur- 
Tents more irresistible than the firebrand of Ulysses. As the as- 
tronomer, however, cannot command a tempest to clear his atmos- 
phere nor a thunder-storm to purify it, his only alternative 1s to 
Temove his telescope to some southern climate, where no clonds 
-@isturb the serenity of the firmament, and no changes of temper- 
ature distract the emanations of the stars. A fact has been re- 
cently mentioned, which entitles us to anticipate gréat results 
‘bumen so instantaneously, as to confirm the remarkable discovery , 
- occupied in publishing. Threatened with a calamity which the- 
ay 
es which will immortalize his own name and add to the scientifig 
Rae ‘te; : 
5 _ Was checked by: the imperfections of the instruments themselves ; — 
’ 
