220 ANNUAL RECOBD OF SCIENCE AND INDUSTRY. 



camp by .1 portable transit; and from the line so established 

 the azimuth of the course was taken by the theodolite and 

 preserved by back-sights on the march. Sketches, geolog- 

 ical notes, and meteorological observations were also taken, 

 and some meagre collections in natural history were made. 

 The botany has been reported upon by Drs. Wilcox and 

 Wood, the insects by Mr. Strecker, and the geology by Lieu- 

 tenant Ruffner, of the Engineers, who conducted the explora- 

 tion. 



The field-work of Mr. King's survey of the fortieth paral- 

 lel was finished several years ago. The oftice-work still con- 

 tinues, but will soon be completed. The entire publication 

 will consist of seven quarto volumes and an atlas, all of 

 which have been published, with the exception of the first 

 volume, on Systematic Geology, by Mr. King (the manu- 

 script of which is ready), and the last on Vertebrate Pale- 

 ontology, by Professor Marsh, which it is hoped will be fin- 

 ished the present year. 



The survey of the Great Lakes and of the Mississippi River 

 is also under the charge of the Engineers. The reconnois- 

 sance for primary triangulation has been extended from 

 Cleveland, O., to the west end of Lake Erie, and the read* 

 ings of the angles of this triangulation have been continued 

 from Painesville to Cleveland. A beginning has also been 

 made upon the triangulation which is to connect Lake Mich- 

 igan and Lake Erie, stations having been erected for one 

 hundred miles east from the southern end of Lake Michigan. 

 At the same time the topography and hydrography have 

 been carried from Vermilion, O., to the western extremity 

 of Lake Erie, and the measurement of a primary base-line 

 with the new Repsold apparatus, begun at Summit, 111., was 

 finished last summer. Astronomical work has also been con- 

 tinued at the observatory of the survey at Detroit, in deter- 

 mination of points in aid of the state survey of Michigan. 

 Observations have been made to determine the height of the 

 lakes. For this purpose a line of levels of precision has been 

 run independently, in duplicate, from Escanaba, at the north 

 end of Green Bay, to Marquette, on the adjoining shore of 

 Lake Superior, a distance of sixty-five miles. The two lines, 

 on reaching Marquette, differed by 31.4 millimeters, and at 

 no point was the difference greater than 41.8 millimeters. 



