AND RATIO OF THEIR ATOMIC WKKillTS. 



29 



the pointer of the balance moves. Through the othei', the observer could watch 

 the vilwations of the balance with very little possibility of disturbance of its indi- 

 cations by his pi'esence. The arrangement is shown in Figure '.), which is in |>arta 

 section from the front to the rear of the balance through its (centre. With this 

 arrangement, it became certain that most distui'bances were due to causes affecting 

 the globes. 



The inside of the case, seen in Fig. 10, was, therefore, lined with sheet metal, so 

 as to lessen the entrance of air curi-ents through the joints of the woodwork. 

 But the opening for an instant of the room in 

 which the balance stood, so as to admit warmer 

 or colder air, would in a few minutes disturb the 

 indications of the balance, not of course by chan- 

 ging the temperature within the case, but by pro- 

 ducing currents of aii' in the room which pene- 

 ti-ated the case and affected the globes unequally. 

 Then the remaining joints in the woodwork around 

 the doors were closed ^during a weighing by past- 

 ing paper over them ; this lessened the disturb- 

 ances, but not sufficiently. A metal box was then 

 made, seen in Fig. !•>, which had a cover with two 

 openings for the suspension of the globes, but had 

 no opening except at the top. The globes being 

 put in this box, it was covered, and placed in 

 the non-conducting case mentioned before, and the globes were hung on the balance. 

 Since the only openings of this box were at the same level, and were small and 

 symmetrically placed, it was hoped that the entrance into it of the air currents due 

 to the motion of the air in the room would be mostly prevented, so that there 

 would remain only the disturbing influence of the convection currents pi-oduced 

 within the box itself by dift'erences of tempei-ature. This hope seemed to be justi- 

 fied, for weighings of the globes placed within tin; l)ox had a mean eri'or not large)- 

 than in the case of objects of the same mass, but far less bulk. The box contained 

 calcium chloride for drying somewhat the air which surrounded the globes. It was 

 not till the art of quickly weighing a globe had been learned by some months of 

 trial that experiments on oxygen or hydrogen were made. 



The globe containing the gas to be weighed was always suspended, in this 

 series of experiments, from the left pan of the balance, and the weights required to 

 pi-oduce equilibrium were also placed on the same pan. After an hour, three suc- 

 cessive excursions were noted, the balance was arrested, and the observation 



Fn;. 9. — Balance siirroundeii with non- 

 conducting case ; illumination of 

 scale and pointer. 



