( 69 ) 
M,= +%M,. 
The meaning of this is that the ions move in circles perpendicular 
to the lines of foree, the direction of this motion being opposite in 
the two cases, represented by the two outer lines of the absorption- 
triplet. 
The assumptions we have found neeessary in the foregoing con- 
siderations, viz. that the inequalities 
Gg! 
Ge and =k RDS 
vy 
exist in a high degree, imply that # A is much larger than 9? J, . 
If this is to be the case, it follows from (18) that EA Lv? must 
. €” 
far surpass %,; in the language of the electromagnetic theory of 
light this means — as may be seen from (14) — that 
hk 
4nve Ne 
must largely exceed the time >. 
Of course this condition can always be fulfilled if only the num- 
ber of molecules N can be made small enough. This was to be ex- 
pected because at very smail densities the molecules must become 
independent of one another, and this is precisely what is assumed 
in the elementary theory. 
It would be difficult to state accurately at what density the expres- 
sion (28) becomes so large that distinct triplets may be seen. The 
preceding considerations show however that the triplets must appear 
in all cases where the observations along the lines of force give « 
good deublet. 
Astronomy. — ‘On the finding back of the Comet of Houmes 
according to the computations of Mr. H. J. Zwiers.” By 
Prof. H. G. VAN DE SANDE BAKHUYZEN. 
In the Transactions of the Royal Academy of Sciences 1st Section 
Vol. IIL appeared a paper by Mr. H. J. Zwiers on the orbit of 
the comet of Hormes, observed from Nov. 8 1892 till March 
13 1893. From these observations Mr. Zwiers has deduced with 
great care the most probable orbit, which proved to be an ellipse, 
in which the comet at its greatest distance from the sun approaches 
