( 588 ) 
Such phenomena may be caused by refraction, whereas hitherto 
the only possible explanation was sought in the assumption of 
tremendous velocities in the line of vision. 
The foregoing considerations may suffice to show that anomalous 
dispersion naturally accounts for a great number of solar phenomena. 
At any rate no future theory of the sun can ignore the laws of 
refraction. 
Physics. — “On the critical isothermal line and the densities of 
saturated vapour and liquid in isopentane and carbon dioxide.” 
By Dr. J. B. VeRSCHAFFELT (Communication N° 55 from 
the Physical Laboraty at Leiden by Prof. H. KAMERLINGH 
ONNES). 
(Read March 31, 1900). 
To be able to deduce from my researches on the capillary ascen- 
sions near the critical temperature !) the surface tension I laid down 
the empiric formula: 
Ol — Ov = 0,243 (1 — m)0,367 
which fairly well represents the densities of liquid g; and vapour ¢@, 
of carbon dioxide at the absolute temperature Z and the reduced 
1 . . . 
temperature m= = given by AMAGAT. This is not the case for 
k 
the temperatures T= 0°,1, r= 0°,35, T= 0°,85, (supposing t = 7,—T) 
in which 
A log (gi—@v) 
A log 7 
= 0,521 between 7 = 0°,1 and 0°,35 
0,468 rr SD sie 
(see Comm. NO. 28 p. 12). In order to represent the interpola- 
tion-curve given by AMAGAT by my formula, it would in this region 
be necessary to raise the exponent of (1 — m) in this formula from 
0.367 to for instance 0.5, the value occurring in the formula 
OL — Qo = A (1—m), which has been deduced theoretically by vaN 
DER WAALS, and given empirically by CAILLETET and MATHIAS. 
This deviation might as remarked in Communication N°. 28, be 
caused by the fact that AMAGAT, without giving a satisfactory 
experimental proof for it, has rounded off his interpolation-curve 
1) Comm. from the Phys. Lab. at Leiden N°. 28, Dr. J. E. VerscuHarreLT. Measu- 
rements on the capillary ascension of liquefied carbon dioxide near the critical temperature. 
