did 
(19 ) 
relatively very small (the weight of the value found for 1862 is in 
fact about zero) and that the values continually oscillate round the 
horizontal line of 759. Sixteen times the latter is intersected by 
the connecting lines, fourteen times this is not the case. There is 
no indication of systematical errors of any importance and I believe 
I am justified in declaring that system II satisfies all just claims. 
For a comparison with future observations I have deduced an 
ephemeris, an extract of which follows in the subjoined table: 
Date § | r Date 6 | # Date 9 r 
1896.0 | 205953 | 3”60 | 1900.5 | 140964 | 4177 | 1905.0 | 107917 | 6'80 
55 L96CG1 1.3. 71.0, V90L0.| 185,60 |, 4:97 .5 | 104 67 | 7.03 
1897.0 | 188.14 | 3.80 ‚5 | 180.97 | 5.18 | 1906.0 | 102.34 | 7.26 
.5 | 180.08 | 3.90 | 1902.0 | 126.71 | 5.40 -5 | 100.14 | 7.49 
1898.0 | 172.42 | 4.00 at 1 Val 5.08 | 1907.0) 98.07 | 77k 
bor 165,17. || 4.02) | 1903.0 | 119.16.) 5.86 „el 96,12) 7.98 
1899.0 158.36 | 4.26 .5 | 115.82 | 6.09 | 1908.0 | 94.27 | 8.14 
‚5 | 152.00 | 4.41 f 1904.0 | 112.72 | 6.33 ‚5 | 92.62 | 8.35 
1900.0 | 146.10 | 4.58 ‚5 | 109.85 | 6.56 | 1909.0 | 90.85 | 8.56 
The parallax of Sirius has been determined very accurately by the 
heliometer measurements of GiLL and ELKin at the Cape in the 
years 1881—83 and 1888—89. If we take with Ginn 0 374 + 0'006 
for the mean according to the weights (M. N., Jan. 1898, p. 81), 
we shall find for the sum of the masses of the two stars 3.51 times 
that of the sun, of which, according to Auwers (l.c. page 231) 
somewhat over °/3 is due to Sirius itself. 
Physics. — “Measurements on the magnetic rotation of the plane 
of polarisation in oxygen at different pressures.” By Dr. L. 
H. Srertsema. (Communication N°. 49 from the Physical 
Laboratory at Leiden, by Prof. KAMERLINGH ONNES). 
The results of my measurements on the magnetic rotation of the 
plane of polarisation in some gases, made at a pressure of about 100 
atm., agreed fairly well with those made by Kunpr and RÖNTGEN '). 
1) Arch. Néerl. (2) 2, p. 878 (1899); Comm. Phys. Lab, Suppl. 1. 
