492 TRANSACTIONS OP THE AMERICAN INSTITUTE. 



about half full, and pi'esented a semi-circle of nearly two feet in diameter* 

 The whole of this surface was pictured with great vividness, covered with 

 long' ranges of mountains, or dotted with huge volcanic summits into the 

 depths of which one could look down. From one of these central points the 

 lava streams could be traced for some eight inches, which, as an inch iu 

 length in the picture corresponds to a hundred miles upon the moon's sur- 

 face, afforded occular evidence of volcanic agency through a line of eight 

 hundred miles. From another, vast fissures were seen to radiate, which 

 displa3''ed evidence of convulsions reaching through an area of half that 

 diameter. Wlien it is considered that the largest photographs hitherto 

 obtained of the moon are not more than from four to six inches in diameter, 

 it will be perceived how great a triumph has been achieved by the science 

 and skill which have been requisite for so great an improvement as a 

 picture of twenty-two inches across. With the utmost patience and persever- 

 ance, and with every appliance of ingenuity, Dr. Draper has continued his 

 work through a series of 3'ears, until he has produced pictures which far 

 surpass the best achievements of European science in celestial photography. 

 There is not another observatory in the world where any similar work can 

 be done. Henceforth the world must look to America for its best views of 

 the heavenly bodies, and the name of the young observer whose care and 

 devotion have accomplished these brilliant results will have an honorable 

 place in the history of the most beautiful department of astronomy. 



Mr. Johnson. — It is stated in the description just read, that to corres- 

 pond to the rate of the moon's motion, which would pass across the field in 

 four minutes, but one ounce- is moved instead of half a ton. I would like 

 to know the size of the negative. 



The Chairman. — Dr. Draper told me it was an inch and a half in diameter. 



Mr. G. Bartlett. — Was the silver deposited on the rear of this reflector, 

 or on its surface? 



Mr. J. Johnson. — It is deposited on the surface, and the thickness of this 

 silver is but the 200,000th of an inch, which has to be slightly polished. 



The Chairman. — In this country probably more discoveries will be made 

 in astronomy than in any other, from the fact that we have a clearer sky. 

 We have also many very fine telescopes, some of these are owned by pri- 

 vate individuals. Mr. Clark, of Boston, has just finished an excellent one 

 for Mr. Joseph Dixon of this Institute. Mr. Fitz, of this city, has lately 

 made a very fine achromatic object glass sixteen inches in diameter. The 

 vast benefit to mankind resulting from the discoveries iu astronomy, are 

 hardly appreciated. Our commercial prosperity rests upon the safety with 

 which the ocean can be navigated; the correctness of the ship's chro- 

 nometer and the precision with which the places of the sun and stars are 

 determined, are the skillful mariner's main reliance in reaching the destined 

 port. 



Commodore W. D. Porter. — The expense of experiments in the science of 

 astronomy are so enormous, that it requires a great amount of wealth to 

 undertake them, but, notwithstanding this, there is probably no country in 

 the world that has done so much as our own for this science, that is, in a 

 private way. The largest photograph of the moon which I have seen was 



