192 PROGRESS OF ASTRONOMICAL PHOTOGRAPHY. 



the rough work of having to figure the polisher for itself on every 

 occasion of repolishing." 



In a more private communication to myself on the same subject, 

 Sir John adds that "Mr. De La Rue's machinery, though grounded 

 on Mr. Lassell's rotary principle, is by no means a servile imitation 

 of Mr. Lassell, inasmuch as several distinct improvements have been 

 introduced tending to distribute the polishing action more equally 

 over the whole surface of the metal. One of these improvements 

 consists in his interposition of a plate between the supporting plate 

 and sliding plate of Mr. Lassell's traversing slide, which, being made 

 to revolve, causes the traversing movement of the speculum to take 

 place, not across the same diameter of its area, but at every stroke 

 across a different diameter ; and he also obviates the irregularity of 

 the motion of Mr, Lassell's polisher on its centre, b}' governing that 

 rotation by mechanism, instead of leaving it to be determined by the 

 excess of external over internal friction." 



But it is in celestial photography that Mr. De La Rue has made his 

 most important discoveries, and displayed an unfailing fertility of 

 mechanical invention. Wisely acknowledging the growing vastness 

 of the several departments of the same science, he has latterly, in a 

 great measure, restricted his researches to the delineation of the 

 various aspects of the heavenly bodies, through the medium of pho- 

 tography. 



It is only by acknowledging and adopting the principle of the 

 division of labor that great results can be obtained, either in the 

 pursuits of commercial industry or abstract science. 



The days of the admirable Crichton have long since passed away. 



Indeed Lord Bacon himself, in the Novum Organum, well observes, 

 in anticipation of the influence of this general principle : 



"Then men shall begin to find out their own powers when all will 

 not essay to do the same things, but each man will employ himself in 

 the work for which he is most apt." * 



Mr. De La Rue's claim to the special notice of astronomers, as a 

 delineator of celestial objects through the medium of photography, 

 does not rest on the absolute priority of his application of a well-known 

 art in a new direction. It is rather based on the fact that by methods 

 and adaptations peculiarly his own, he has been the first to obtain 

 automatic pictures of the sun and moon, sufficiently delicate in their 

 detail to advance our knowledge regarding the physical characters of 

 those bodies, and admitting of measurements astronomically precise. 



The late Mr. Bond, of Cambridge, in the United States, in the 

 year 1845, with the assistance of Messrs. Whipple and Bond, obtained 

 good pictures. of aLyrce and of Castor ; and that, in this year, Signor 

 De Vico made an unsuccessful attempt to photograph the nebulge in 

 0ri07i. 



At about the same time, or a little later, the Rev. J. B. Reade took 

 photographs of a Lyrce at my observatory at Hartwell, and at his 

 own observatory at the Vicarage of Stone. 



* " Tuiu eaim homines, vires suas nosse incipient, cum non eadem iafiniti, sed alia alii 

 prajstabuut " — Liber 1, aphor. cxiii. 



