BAIRD &TATLOCK (LONDON) LTD. 



1773 



1773" Balance, Jolly's Spring, with a series of springs of various strengths, and graduated 

 mirror scale. Mounted on tripod base with levelling screws 



This balance is used for (a) Determination of the weight of small bodies. 



(b) ,, ,, specific weight of solids. 



(c) ,, ,, specific weight of fluids. 



The balance consists of a spring suspended from the top of a sliding support ; the spring carries on its lower 

 end a scale-pan and an index mark above the latter. The support has a mirror millimetre-scale on which the 

 position of the mark can be read without parallactic error. A small glass pan and a solid glass body are to be used 

 as described in the following instructions. A small table to carry a glass vessel filled with water or other fluid 

 slides on the stand, and may be fixed in any desired height. Levelling screws serve to bring the instrument into 

 a vertical position. 



The principle of the balance is founded on the law of elasticity that (within certain limits) the elongation 

 of a spring is proportionate to its load. 



To prevent these limits being exceeded, and to enable the instrument to be used for different loads, a number 

 of springs are supplied with each balance, each spring carrying up to 2, 6, and 10 grammes. 



(a) Determination of Absolute Weight. 



Let the index mark indicate any point " m " of the scale ; if a body is placed in the pan the mark will indicate 

 another point "n." Then m is the absolute weight, measured in divisions of the scale. Should the body have a 

 weight of 5 grammes and stretch the spring f. i. from 150 to 600 millimetres, then an elongation of 



450 millimetres corresponds to a weight of 5 grammes 

 45 ,. 0.5 



4-5 ,. -5 ., 



for the same spring. 



(b) Determination of Specific Weight of Solids. 



Fix the small glass pan below the metal pan ; place a glass vessel filled with distilled water on the sliding 

 table, and during the whole experiment let the glass pan dip into the water, but take care that it does not touch the 

 sides or bottom of the vessel. 



First determine the absolute weight of the body (which must be placed in the upper metal pan) as described 

 above = n n>. Then put the body into the glass pan (dipping into water); the table with the glass vessel must 

 then be raised to a point " p." 



250 



14- -CROSS STREET HATTON GARDEN, E- C 



366 



