90 SEC. 3. MEASUREMENT. 



439. Clinometer of Precision, with improved mounting, 

 readers, and level. Prof. Piazzi Smyth. 



This instrument was made to order by E. E. Sang, of Edinburgh, in 1869, 

 and intended for measuring Great Pyramid angles of slope. It carries its 

 own footbar, 25 inches long, has improved readers and illuminators, and a 

 chloroform level, as being more quick and frictionless than either ether or 

 alcohol. The circle can be rotated and clamped on its own centre for due repe- 

 tition of the angles round the circumference ; the verniers read to 1', and there 

 are supplementary verniers for investigating errors of division. 



440-1. Drawings and Photographs of Dividing Ma- 

 chinery. Messrs. Trouyhton Simms. 



Fig. 1. General view of dividing machine. 



A. The circular table with racked circumference containing 4,320 teeth, 



each tooth, therefore, equal to five minutes of arc. 



B. The screw by which movement is communicated to Table A. 



C. A ratchet wheel attached to the screw shaft. 



D. A crank arm which during one half of a revolution gives a forward 



movement to the screw ; during the remaining part of its revolution 

 the screw is at rest. The axis which carries the crank arm has a 

 bevelled wheel upon it, serving to communicate motion to the 

 cutting apparatus. 



E. The cutting frame. 



F. A cam to give movement to the dividing knife or other tool by which 



the division is made. 



The apparatus is so arranged that the division may be cut whilst 

 the circular table is at rest, the tool being lifted by a second cam (not 

 well seen in the drawing) when the table is in motion. 

 Fig. 2. Plan of cutting apparatus showing the relation it bears to the 

 circular table and screw. 



Fig. 3. Section of table and axis. 



Fig. 4. Drawings of cams and cutting frame, the cam " h " for lifting the 

 tool (just seen in Fig. 1) is here shown. 



442. Clinometers, devised by the Rev. Professor 

 Henslow, one of which was used by Dr. Hooker in his 

 Himalayan journeys. J. D. Hooker, M.D., P. U.S. 



443. Protractor, with scale, vernier, and magnifying glass. 

 Reads to 1 min. Prof* Baron von Feilitzsch, Greifswald. 



443a. Plate Glass Sector, designed for the purpose of 

 plotting angles on plans or charts where it is necessary to see the 

 work under the sector, and the divisions being on the side next 

 the paper no variation in pricking off can take place, 



Thos. F. Chapp. 



443b. Instrument for the Measurement of Angles. 



Dr. Fr. Holler, Selbo Drontheim, Norway. 



