2^2 
LORD RAYLEIGH OH A XFAV MAYOMETER, 
readings oi the higher pressures, where in any case the error would he a smaller pro¬ 
portion ot the whole. Also some of the observations were not repeated. Another 
2 :)oint that may he noted is that the means are chosen with respect to the values of 
and that a different choice would in many cases materially reduce the mean error 
in the last column. 
Having thoroughly tested the a23paratus and the method of exj^erimenting with 
liydrogen and nitrogen, I returned with curiosity to the case of oxygen. Special 
2 )ai 2 is were taken to ensure that the gas should l^e pure and above all dry. To this 
end glass tubes were prepared containing permanganate of potash and phosphoric 
anhydride, and these were connected l)y sealing to one of the l^ranches of the 3-way 
tajD. A liigh vacuum having been made throughout, heat was gradually aiDjDlied, 
and some of the oxygen allowed to blow off. The phosjDhoric tulje (of considerable 
cajjacity) was then allowed to stand full of gas for some little time, after which 
the necessary gas to a jji’^'^sure of about 10 centims. was allowed to enter the 
a 2 ) 2 Jai’atus by means of the 3-way tap. With regard to the maintenance of the 
juirity of the gas under rarefaction, it may be remarked that the method of exjjeri- 
menting was favourable, inasmuch as the last stages were not readied until the 
apparatus had been exposed to the gas under trial for a week or two. Any con¬ 
tamination that might be communicated from the glass during tlie first few days 
would for the most part be removed before the final stages were reached. 
Before the regular series was commenced, sjiecial observations extending over 
several days were made in the region of jiressure (from 1 millim. to '5 niillim.) where 
Bohr found anomalies. No unsteadiness could be detected. Whatever reading 
was obtained within a few minutes of a change of pressure was confirmed after an 
interval of an hour or more. Foi’ exainjile, on November 29, at 12'‘ 25“ the jii’ossure 
which had stood for some time at '80 millim. was lowered to '05 millim. At 8'' 0“ 
the jiressure was unaltered. In no case was the liehaviour in any way different to 
that which had been observed with tlie other gases. It is true that Avhen the 
oliservations were reduced one preliminary set showed an excess of ^.iressure at the 
smaller volumes similar to that recorded in the case of hydrogen, ljut the tendency 
is scarcely visible in the regular series now to be given, which extended from 
November 27 to December 9. 
An examination of the numbers in the Table IX. shows that Boyle’s law was 
observed, })ractically u}) to the limits of the accuracy of the measurements, and in 
particular that there was no such falling off in the value of pv at low 2 )ressures as 
was encountered by Bohr. What can be the cause of the difference of our 
exjDeriences I am at a loss to conjecture. I can only su23|)ose that it must be 
connected somehow with the quality of the gas, conpdicated })erha 2 )S by interaction 
with the glass or with the mercury. 
