Des transactions . 16 ; et M. W. T. Lynn methat informe le premier des portabletype, au meilleur de sa connaissance, d'avant-garde est mentionnée dans le sixthvolume de l'édition de 1 ^-i1de l'encyclopédie d'Édimbourg, où il y a l'illustre une anddescribed-transit portable instrument qui EdwardTroughton conçu en 1810.Dans le même endroit qu'il est un similarone creditedwith ayant arrangé que tar hark comme 171*2. En outre, M. Lynn dit therewas publié dans le Dictionaryof Literatun et Arts, Sciences(Abraham Rees, 1819) anothermodel Troughtons whichhears de, un resemblanceto très proche Youngs. La seule copie

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Transactions . 16; and Mr. W. T. Lynn informs methat the first of the portabletype, to the best of his knowl-edge, is referred to in the sixthvolume of the edition of 1 ^-i1of the Edinburgh Encyclopedia, where there is illustrated anddescribed a portable transit-instrument which EdwardTroughton designed in 1810.In the same place he is creditedwith having contrived a similarone as tar hark as 171*2. Further, Mr. Lynn says therewas published in the Dictionaryof Arts, Sciences and Literatun(Abraham Rees, 1819) anothermodel of Troughtons, whichhears a very close resemblanceto Youngs. The only copy ofthis rare work known to Mr.Lynn is preserved in the BritishMuseum, where they object tohaving reproductions of anykind made, though I hope sub-sequently to prevail upon the Director to extend this courtesy to American students. Thetransit illustrated by Rees has some points in common with thr-one I have selected from 8immss workt and presented in Fig.168. The author does not give the date of its introduction;. 8-inch Alt-Azimuth. * Late of the Royal Observatory ; now residing at 26 South Vale, Blaek-heath, London, S.E. f A Treatise on Mathematical Instruments, F. W. Simms, London ; 1st ed., 1834 ; 5th, 1>44. 926 THE EVOLUTION OF MINE-SURVEY INQ tNSTRUMENTS. but Mr. V. Simms (now retired from tin- firm of Troughton &Bimms) testifies that it was a regular model when he, enteredthe business iii L832. The azimuth-axis of this transit-instru-ment was inverted between the standards, as in one of Mr.Iloskolds instruments; but the pillars were of sufficient heightto permit a complete revolution of the telescope—a desirablefeature not included in the model just referred to (Fig. 75, Trans., xxix., 964). It would be hardly fair, from what I know at this writingconcerning these instruments, to attempt to show that the de-signs prevalent in early English models were in any way re-sponsible for that of Young, particularly as these so-calledaltitude- and azimuth-instruments, with thei

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