116 Winterhalter — Personal Equation Machine. 



The lines given by different observers, however, do not appear 

 to coincide with the prominent lines and bands observed in the 

 air spectrum heightened by steam. 



Other observers, among them Professors Liveing and Dewar, 

 have employed steam to obtain steam lines, but we have been 

 unable to find any reference to the remarkable economy in 

 time and in waste of apparatus which results in the use of a 

 jet of steam in spectrum analysis, when the spark method of 

 obtaining the spectra of metals is employed. 

 Jefferson Physical Laboratory. 



Art. XI Y.— A New Personal Equation Machine, for use 

 with the Meridian-Circle; by A. G-. Winterhalter, Lieut., 



U. S. Navy. 



Doctor Walter F. Wislicenus, in charge of the merid- 

 ian-circle at the Strassburg Observatory, has lately given an 

 account of his investigations, by means of an apparatus devised 

 by himself, of his personal error in recording transit observa- 

 tions. The salient features of the machine are its attachment 

 directly to the meridian-circle and the capability of using it in 

 almost any position of the telescope. These warrant a brief 

 exposition of the contents of Dr. Wislicenus's paper.* 



The idea of determining the personal error in transit obser- 

 vations by means of an apparatus appears to have been first 

 enunciated by Professor Kaiser in 1851 in the 5th volume of 

 the Tijdsschrift voor de Wis- en Natuurkundige Wetenschap- 

 pen. Prazmowski, in Warsaw, seems to have been the first to 

 publish (in Cosmos, vol. iv, p. 445), in 1854, a scheme for a per- 

 sonal equation apparatus. 



The author, after a more or less detailed study of the appa- 

 ratus designed, successively, by Mitchel, Plantamour and 

 Hirsch, C. Wolf, F. Kaiser, E. Kayser, Harkness, Hilgard and 

 Suess, Eastman, R. Wolf, Bredichin, Christie, has arrived at 

 the conclusion that in all previous instruments the disadvantage 

 is presented of a horizontal position of the telescope used and, 

 therefore, of an upright one of the observer, conditions not 

 found in transit observations. From this and other considera- 

 tions, the author lays down the following features to be com- 

 plied with by such an apparatus : 



1. The personal error should be determined with the same 

 instrument with which observations are made. 



* TJntersuchungen iiber den absoluten personlichen Fehler bei Durchgangs- 

 beobachtungen. Von Dr. Walter P. Wislicenus, Privatdocent and Assistent an 

 der Sternwarte zu Strassburg. Leipzig, 1888. Pp. 50, 9"xl2" ; one plate, with 

 3 figures. (Wilhelm Engelmann). 



