Miscellanies. 205 



17. Sketch of the Analytical Engine invented by Charles Babbage, 

 Esq. By L. F. Menabrea of Turin, Officer of the Military Engineers ; 

 with notes by the translator. (Extracted from the Scientific Memoirs, 

 Vol. 3.) London, 1843.— It is well known that in 1823 the British 

 government undertook to construct a calculating engine invented by 

 Mr. Babbage. This machine was designed to compute and print off 

 tables of many different kinds, particularly such as are wanted for the 

 uses of astronomy and navigation. The calculations were to be per- 

 formed by the successive addition of finite differences, a method which 

 admits of rigorous exactness, only where all the differences after a 

 certain order (in Mr. B.'s machine the seventh) disappear, but which 

 in many other cases is able to furnish within certain limits results ac- 

 curate enough for every practical purpose. The construction of this 

 machine, after ten years' labor and an expenditure of =£17,000, was 

 discontinued in 1833, and has never since been resumed. Shortly af- 

 ter this interruption, Mr. Babbage conceived the plan of a machine 

 essentially different from his first, possessing all its powers, and others 

 vastly more important ; which, instead of being confined to arithmet- 

 ical addition, should be able to add, subtract, multiply, divide, calculate 

 powers and roots, in any required order of succession, and in strict 

 obedience to the laws of algebraical combination. Of this stupendous 

 invention Mr. Menabrea has given us an account, remarkable for its 

 clearness, and, so far as it goes, satisfactory. Avoiding all detail, he 

 presents in distinct though general outline, the plan of the machine, 

 and its mode of operation. Much valuable information and explanation 

 are supplied by the copious notes of the translator. 



MISCELLANIES. 



DOMESTIC AND FOREIGN. 



1. Dr. Percival, the original observer of the crescent-formed Dykes 

 of Trap in the New Red Sandstone of Connecticut. — At the last meet- 

 ing of the Association of American Geologists and Naturalists, held at 

 Albany, in May, 1843, a discussion arose on the cause of the crescent 

 form observed by Dr. Percival in the trap dykes of the Connecticut 

 sandstone, and by Prof. H. D. Rogers in the same formation in New 

 Jersey. A condensed summary of this discussion is given on page 334, 

 Vol. xlv, of this Journal. 



Prof. Rogers introduced his remarks by saying, that his attention 

 had been arrested on examining the singularly accurate and beautiful 

 map by Dr. Percival, published in his Report on the Geology of Con- 



