INSTRUMENTS. 



The instruments of the expedition were the property of a member of the 

 party, and were as follows : 



TRANSIT. The transit was made by Messrs. Heller & Brightley, of Phila- 

 delphia, and is a fac- simile in miniature of their " complete engineer's transit." 

 It is one of the instruments exhibited by this firm at the Centennial Exhibition 

 in Philadelphia, where it took a prize. It has long compound centres, the 

 vernier plate centre being 2^ inches long. The horizontal limb is read, by two 

 double opposite verniers, to minutes of arc. These verniers are placed outside 

 of the compass-box, and their openings are protected by glass windows. The 

 vertical arc also reads to minutes. There is a 2^-inch magnetic needle, and its 

 ring is divided into half degrees. The telescope is 6f inches long, with object- 

 glass H inch in aperture ; it magnifies 15 diameters, and shows objects erect, 

 not inverted. A sensitive level 3 inches long is attached to the telescope for 

 assistance in accurate levelling work. The telescope has a slow motion for 

 focussing the cross wires, and is provided with adjustable stadia wires for 

 measuring purposes, thus dispensing with chaining and taping to a consider- 

 able extent. The plates and vertical circle are provided with clamp and tan- 

 gent screw movements, and the clamps on the axis of the telescope are 

 arranged with sighting slits and indexes, so as to answer also for right angle 

 sights. All the working parts of the needle-lifter, clamp and tangent screw 

 movements are concealed between the plates, making the instrument more 

 compact and less liable to injury. The height of the instrument from the tripod 

 legs is 7| inches. The extreme diameter of the plates is 4! inches. The 

 diameter of the horizontal plate at the point where the verniers and graduation 

 meet is 3$ inches. The tripod is furnished with an adjustable head for precise 

 plumbing over a centre. The weight of the instrument exclusive of tripod head 

 and legs is 5 Ibs. The weight of the tripod is 3 Ibs. The instrument, with its 

 various additional parts (such as sun-tube, screw-drivers, magnifier, etc.), is 

 packed in a box 8 inches long, 5 inches wide, and y inches deep. This box is 

 arranged with straps to allow of its being carried over the shoulder. The con- 

 stant to be added to every recorded stadia reading of this instrument was ob- 

 tained as follows : Object focal length, 4$ inches ; object-glass to centre of 

 instrument, 3f inches. Hence, if 8 inches be added to the stadia measure- 

 ment, the measurement will then be to the centre of the instrument or plummet. 

 We found this instrument reliable, its graduation very good, and the power of 

 its telescope remarkable. 



SEXTANT. The sextant was one of Stackpole's best. It reads to 10" of arc, 

 and was provided with all the accessories usually accompanying such an instru- 

 ment. The pocket sextant was made by James Green, of New York, and read 

 to minutes of arc. Both these instruments did good service. 



BAROMETERS. The two mercurial and two aneroid barometers used were 



