Obituary. Professor Wallace. 535 



tograph, he invented, in 1821, an instrument on a different principle 

 to supply its place, to which he gave the name of Eidograph. This 

 instrument answers the same purposes as the common pantograph, to 

 which, however, it is greatly superior, both in the extent of its ap- 

 plications and the accuracy of its performance ; for while the simi- 

 larity of the copy to the original, in all its parts, is preserved with 

 geometrical accuracy, the copy may be reduced or enlarged in almost 

 any proportion ; or, by a particular modification of the instrument, 

 it may even be reversed, and transferred immediately to metal or 

 stone. This ingenious instrument, which would seem to be admirably 

 adapted to the purposes of the engraver, was first described by him 

 in vol. xiii. of the Edinburgh Transactions, to which reference has 

 already been made. He has also described, in the Appendix to his 

 Conic Sections, an Elliptograph, or instrument for describing an 

 ellipse by continued motion, founded on a very beautiful property of 

 the ellipse first pointed out, we believe, by him, namely, that the 

 curve is organically described by any given point (not in the circum- 

 ference) in the plane of a circle which rolls along the concave cir- 

 cumference of another fixed circle, the radius of which is twice that 

 of the rolling circle. And in an Appendix to his Geometrical Theo- 

 rems he has given the description of an instrument which he invented 

 for the graphical solution of an important problem in surveying, viz. 

 to determine the position of a station, having given the angles made 

 by lines drawn from it to three other stations in the same plane, 

 whose positions are known. This instrument, which he called a 

 Chorograph (the problem which it solves having been proposed as a 

 chorographical problem by Richard Townley in No. 69 of the Philo- 

 sophical Transactions), is simple, compact, portable, and inexpensive ; 

 and in these respects has considerable advantages over the station- 

 pointer, generally used for the same purpose. 



Among the objects connected with the advancement of science to 

 which Professor Wallace gave his aid, after his appointment to Edin- 

 burgh, there is one which it would be unpardonable to pass over 

 without notice in this place, — we allude to the observatory now esta- 

 blished there. Ever since the time of Maclaurin there had existed 

 a small astronomical observatory in Edinburgh, but no provision was 

 made for regular observation, nor, indeed, did it contain any instru- 

 ments fit for the purpose. Through the exertions, chiefly of Pro- 

 fessor Playfair, funds were at length raised, by private subscription, 

 for the erection of an observatory adapted for observations of the most 

 accurate kind. Mr. Playfair did not live to see the building completed, 

 or means provided for obtaining instruments, or carrying on syste- 

 matic observations ; but Mr. Wallace, on becoming his successor, 

 entered fully into his views, and, in concert with a few other indi- 

 viduals, used all his influence and exertions towards bringing the 

 scheme to maturity. At length, after years of expectation and delay, 

 the Government was prevailed upon to take the observatory under 

 its protection, furnish it with instruments of the first class, appoint 

 an astronomer and assistant, and provide for the regular publication 

 of the observations. In bringing about this arrangement, Mr. 



