ASTRONOMICAf. DISCOVERIES, 33 



it is brushed over with a solution of the gallo-nitrate of silver in acetic 

 acid, formed by adding to acetic acid nitrate of silver and gallic acid. — 

 The whole of the preparation of the paper must be conducted in the dark 

 or by candle-light. This paper may be used after being carefully dried by 

 gentle warmth or whilst it is yet moist. It must be carefully kept from 

 the light, for even the light of the moon makes a sensible impression 

 upon it. When used, it is introduced, for a few seconds into the cam- 

 era, as in the Daguerreotype ; then, as the image is not yet visible, it is 

 brushed over again with the gallo-nitrate of silver, and warmed before 

 a fire, when the picture will immediately begin to appear on the part ex- 

 posed to the image of the camera. To prevent the other part of the 

 paper from blackening and to fix the picture, it is dipped into a solution 

 of the bromide of potassium, which removes all the salt of silver which 

 has not been altered by the light. 



ASTRONOMICAL DISCOVERIES. 



BY DANIEL KIRKWOOD, OF LANCASTER, PA. 



At the beginning of the seventeenth century, but few, even of the 

 learned, had adopted the system of astronomy taught by Copernicus ; 

 and to these, no more than seven planetary bodies were known ; viz.. 

 Mercury, Venus, the Earth, the Moon, Mars, Jupiter and Saturn. Mad 

 the most enthusiastic astronomer of that day been told that in less than 

 two centuries and a half this number should be quadrupled, he would 

 doubtless have regarded the idea as visionary and extravagant. Such, 

 however, has been the fact. Aided by modern instruments, we can now 

 number thirteen primary and eighteen secondary planets. In view of 

 these mighty achievements of science, who will presume to say how 

 much the restless energies of the hnman mind may yet unfold, even 

 within the limits of our own system, in a century or two to come ? 



On the 8th of January, 1610, Galileo, "the Columbus of the 

 Heavens," discovered the satellites of Jupiter. This was his first great 

 discovery by means of his newly invented telescope. So great, at that 

 time, was the geneial prejudice against the Copernican system, that some 

 of its opponents, determined to reject whatever might be regarded as 

 militating against their own views of the universe, even denied the truth 

 of the revelation made by tlie Tuscan glass, thus refusing to admit the 

 evidence of the sense of sight. The following is a specimen of the logic 

 by which Galileo was opposed: "There are seven windows given to 

 animals in the domicil of the head, through which the air is admitted 

 to the tabernacle of the body, to enlighten, to warm, and nourish it; 

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