208 
LOED KAYLEIGII ON A NEW MANOMETEE, 
So far as I am aware, no attempt to repeat Bohr’s difficult and remarkable experi¬ 
ments lias been recorded, but some conffi-ination of anomalous behaviour of oxvo-en in 
this region of pressure is afforded by the observations of Ramsay and Baly."^ 
SuTHERLANDt iutei'prets the results as a “ Spontaneous Change of Oxygen into 
Ozone and a Btemai'kable Type of Dissociation,” and connects tbere^Yith some 
o])servations of Crookes relating to radiometer effects in oxygen gas. (3n the other 
hand, chemical tests applied by Professor Threlfall and Miss Martix;*; failed to 
indicate the presence of ozone in suitably expanded oxygen. 
Improved ApjKiratus for Measurvng very small Pressures. 
In spite of the interest attaching to the anomaly encountered by Bohr, I should 
hardly have ventured to attack the question experimentally m^^self, had I not 
seen my way to what promised to be an improved method of dealing with very 
small pressures. In operations connected with the weighing of gases, extending 
over a series of years, I liave had much experience ot a specially constructed 
manometric gauge in which an iron rod provided above and below with suitable 
points is actually a})plied to the two mercury surfaces arranged so as to be situated 
in the same vertical line.§ Although tivo variable quantities had to be adjusted— 
the pressure of the gas and the supply of mercury—no serious difficulty was 
encountered ; and the delicacy obtained in the observation of the approximation of 
a point and its image in the mercury surface with the assistance of an eye-lens of 
25 millims. focus was very satisfactory. In order to get actual measures of the 
delicacy, a hollow glass apparatus in the form of a fork was mounted upon a levelling 
table. The stalk below was terminated with a short length of rubber tubing 
compressible by a screw. This allowed the supply of mercury to be adjusted. The 
mercury surfaces in the U were about 20 millims. in diameter, and were exposed to 
the air. They were to be adjusted to coincidence with needle points, rigidly 
connected to the glass-work, by suitable use of the conqDressor and of the screv' of 
the levelling table. Readings of the latter in successive and independent settings 
showed that a degree of accuracy was attainable much superior to the limit fixed 
by Amagat for the best work with the cathetometer. It is unnecessary to record 
tiie numljers obtained at tliis stage of the v'ork, inasmuch as the final results 
to be given below prove that the errors of setting are considerably less than 
ToW millim. 
It will now be possible to form a preliminary idea of the proposed manometer. 
Tlie readings of the levelling screw, obtained as above, may be regarded as corre- 
* ‘ Phil. Mag.,’ vol. 38, p. 301, 1894. 
t ‘ Phil. Mag.,’ Yol. 43, p. 201, 1897. 
1 ‘ Proc. Eoy. Soc. of New South tVales,’ 1897. 
^ “On the Densities of the Ih'iiicipal Gases,” ‘ I’roe. Eoy. Soc.,’ yuI 53, p. 134, 1893. 
