BAIRD &TATLOCK (LONDON) LTD. 



THE THEODOLETTE. 



Patent No. 15472. 

 New Instrument for Land and Mining Surveyors, Civil Engineers, etc 



Illustrations about two-thirds full size. 



880 



>7 T A surveying instrument of small and compact dimension, capable of fulfilling many 

 requirements, is a great desideratum, and the instrument described below has been 

 invented to facilitate the taking of angular measurements, either horizontally or 

 vertically, with accuracy and despatch hitherto only obtainable with the larger and 

 more_expensive instruments. Complete with leather sling cases 



The instrument measures 7 in. by 3 in. by ij in., and weighs thirteen ounces. The body contains a clinometer disc and a 

 .pass dial, both of aluminium, divided on the periphery into half degrees, being read through a telescope of strong power, 

 bling the observer to obtain very accurate results. The face of the clinometer disc is divided into degrees, and has a proportion 

 le for determining heights and setting-out levels. The scales are read through a window over the face of the disc. The compass 

 1 is divided on the face to every five degrees, figured every 20 to 360, and 8 compass letters for use as an ordinary compass, 

 o levels are mounted on a loose collar, rotating on the body of the telescope ; these are for the purpose of levelling the instrument, 

 en in the horizontal (Compass, Fig. i) or vertical (Clinometer, Fig. 2) position. A screwed socket is fitted for attaching the 

 rument to the double action head of a light but rigid aluminium telescopic stand. A foot is also attached, so that the instrument 

 be used for ascertaining or setting out angles of slope on surfaces. When once the instrument is set up, forward or backward 

 lings can be taken by simply turning the instrument end for end. 



For Finding Heights of Buildings, etc. The instrument is aligned on the objective, and a note made of the division on the 

 roportion ' ' scale that cuts the index line on glass. The distance from observer's position to base of the objective is now measured 



the distance divided by the figure noted ; the result, plus height of observer, is the height required. For instance, supposing 

 index line cuts division 3, and the distance is 150 ft., 150-^3 = 50 ft. + height of observer = height of object. 



The following tables will be found of much assistance. Table A gives certain angles of elevation or depression, which give 

 :y of rise per amount of run. Thus 18 deg. of elevation gives i vertical to 3.0 horizontal. Table B gives certain angles up 

 5 deg., the amount of rise or fall per 100 of run, measured horizontally. Heights can therefore be found as follows : Thus, 

 4 deg. of elevation the rise would be 7.0 per 100 horizontal, and an object 300 ft. from the observer, extending an angle of 

 e. would be 7.0 X 3 = 21 ft. in vertical height. 



TABLE A. 





CHEMICAL AND SCIENTIFIC APPARATUS AND PURE CHEMICALS- 



