III. SURVEYING. 741 



3153e. Two Cases of Instruments used by the late Cap- 

 tain Speke in Africa, with map of his discovery of the region of 

 the Nile sources. William Speke, jun. 



3027a. The First Traces ever found of the Franklin 

 Expedition. Admiral Ommanney. 



a. THEODOLITES. 

 3039. Five-Inch Theodolite by Adams. Royal Society. 



3047. Theodolite with 3-inch circle. 



Messrs. Troughton 8f Simms. 



The telescope is of the bent form, having a small rectangular prism in the 

 axis. The light received by this prism is turned through the axis of the 

 instrument, and an image of the object is formed outside the pivot. By this 

 construction the instrument may be kept low, and possess at the same time 

 considerable optical power. 



3047a. Five-Inch Theodolite. Joseph Casartelli. 



In makiag this theodolite the object has been to reduce the number of 

 parts and simplify the construction. It has double conical bearings to the 

 axes, with a ball-and-socket adjustment, and spring verniers to the horizontal 

 circle, producing an easy and smooth motion. The whole is made of gun- 

 metal. 



3047b. Travellers' Transit Theodolite and Stand. 



Improved by the late Lieut.-Col. Strange, F.R.S., and adapted 

 for alpine and military surveys or occasional astronomical obser- 

 vations. L. Casella. 



3047c. Travellers 9 Transit Theodolite and Stand, with 

 telescope in centre. Improved by the late Lieut.-Col. Strange, 

 F.R.S., and adapted for alpine and military surveys or occasional 

 astronomical observations. L. Casella. 



3047 d. Gary's Improved 5-in. Theodolite, with im- 

 proved rack adjustment to cross webs of eyepiece, and improved 

 form of tripod foot. Henry Porter. 



3048. Theodolite (10*5 in.), in which the vertical arc is 

 jointed on an ordinary sector, and covered with a variety of scales. 

 Made by Sissons, London. Major M. L. Taylor, R.A. 



304:9. Repeating Theodolite, horizontal circle 14 cm. in 

 diameter, divided to 20' reading to 30" by vernier. The divided 

 limb is completely covered and the verniers are protected by glass 

 plates. Telescope, 12 lines free aperture, magnifying 25 times, 

 vertical circle divided to 30' reading to 1' by vernier. Level to 

 arrange the telescope in two positions. A. and R. Hahn, CasseL 



