Mr. J. Phillips on a Drawing of ' Copernicus' 475 



enough to be transferred from photography* to any kind of en- 

 graving, but I am watching every good occasion to make it complete. 

 But before bestowing more time and labour, I should be glad to 

 know the impression such a work may make among the scientific 

 men of England. I must observe that the most distant outliers of 

 the crater have not been included," &c. 



" Notes on the Drawing of * Copernicus,' presented to the Royal 

 Society by P. A. Secchi." By John Phillips, Esq., F.R.S. 



Of the few attempts which have been made of late years to pre- 

 pare drawings f, on a large scale, of selected lunar mountains, this 

 contribution from the Roman Observatory appears to be one of the 

 most successful. It is on a scale of magnitude (about 10 geogra- 

 phical miles to one inch) such as only the larger modern telescopes 

 can command, and characterized by such firmness of definition as to 

 do honour alike to the maker of the instrument and to the artist 

 engaged in the delineation. It may assist those who have not 

 attempted, with their own hands, any drawings of this kind, and 

 desire to form a right judgement of the value of this work of 

 P. Secchi, if I send for comparison a drawing of Gassendi, executed 

 from my object-glass of Q\ inches (Cook), with a focal length of 

 1 1 feet. The drawing is on a scale of 20 geographical miles to an 

 inch, and Gassendi thus appears of half the linear dimension of 

 Copernicus, being really almost of the same diameter. > 



Placing together the two drawings, and remembering the appear- 

 ance of Copernicus, as I have seen it through telescopes, some re- 

 flections arise which it may be permitted me to express, in the hope 

 that we are now fairly entered on the long career of discoveries in 

 the moon, to which the attention of astronomers has been of late 

 systematically drawn by the Earl of Rosse and a Committee of the 

 British Association. 



In proportion as the power of the telescope rises, the seemingly 

 simple *ring mountains' of the moon exhibit as much diversity of 

 outline and structure as the larger terrestrial volcanoes when accu- 

 rately mapped. Thus while Gassendi, — 40° from the central meri- 

 dian of the moon, and 17° south | of the equator, — has the obliquely 

 elliptical contour due to a circle in that position, Copernicus, 20° 

 from the central meridian, and 10° north of the equator, has its 

 most conspicuous peripheral crest formed of seven principal nearly 

 straight elements, approaching to equality in length, and meeting in 

 points which are situated almost exactly in a circle of 24 geographical 

 miles radius. Here is a very important partial difference, coupled 

 with a very important general agreement. 



While Gassendi, with peaks 9000 feet high, projects like a huge 

 narrow wall into the Mare Humorum, and hangs over the interior 

 plain in precipices as steep and many times as high as those over the 



* The figure presented to the Society is a photographic copy of the origin^ 

 drawing. — (Ed.) 



t As distinct from m&te plans. The drawings must however be based on exact 

 plans. - 



X The Poles being named after the type of Madler's noble work, * Der Mond.' 



213 



