AucustT 3, 1899] 
NATURE 
319 
be separated, and I have endeavoured to show its 
migrations and gradual concentration as the work pro- 
gresses, by tinting the fractions where it mostly would 
concentrate, the depth of tint representing the amount 
of concentration. 
In the purest condition yet obtained victoria is an 
_ earth of a pale brown colour, easily soluble in acids. It 
is less basic than yttria and more basic than most of the 
earths of the terbia group. In chemical characters it 
differs in many respects from yttria. From a hot nitric 
acid solution victorium oxalate precipitates before yttrium 
oxalate and after terbium oxalate. On fractional pre- 
cipitation with potassium sulphate the double sulphate 
of victorium and potassium is seen to be less soluble 
than the corresponding yttrium salt, and more soluble 
than the double sulphates of potassium and the terbium 
and cerium groups. Victorium nitrate is a little more 
easily decomposed by heat than yttrium nitrate, but the 
difference is not sufficient to make this reaction a good 
means of separating victorium and yttrium. Fusing the 
nitrates can, however, be employed advantageously to 
separate mixed victoria and yttria from the bulk of their 
associated earths. 
On the assumption that the oxide has the composition 
Vc.O,, the atomic weight of victorium is apparently not 
far from 117. 
The photographed phosphorescence spectrum of vic- 
toria consists of a pair of strong lines at about A 3120 
and 3117 ; other fainter lines are at 3219, 3064, and 3060. 
Frequently the pair at 3120 and 3117 merge into one, 
‘but occasionally I have seen them quite distinct. The 
presence or absence of other earths has much influence 
on the sharpness of lines in phosphorescent spectra, and 
it is probable that these lines will be sharp and distinct 
when victoria is obtained quite free from its associates. 
The best material for phosphorescing in the radiant 
matter tube is not the earth itself, but the anhydrous sul- 
phate formed by heating the earth with strong sulphuric 
acid and driving off the excess of acid at a red heat. The 
sulphate thus produced, prebably also containing some 
basic sulphate, is powdered and introduced ito a bulb 
tube furnished with a quartz window, and a pair of thick 
aluminium poles sealed into the glass with stout platinum 
wires. The tube is well exhausted, keeping the current 
from a good induction coil going all the time. The 
pumping and sparking must continue until the earth 
glows with a pure light free from haze or cloudiness, and 
‘continues so to glow during the passage of the current 
without deterioration. The exposure in the spectrograph 
usually occupies an hour. 
I give a diagrammatic plan of the two-prism spectro- 
graph used in this research. It is furnished with two 
quartz prisms, quartz lenses and condensers. The slit 
jaws are of quartz, cut and polished according to the 
method I described in the Chemical News, vol. Ixxi. p. 
175, April 11, 1895. 
The prisms are made in two halves according to 
‘Cornu’s plan, one half of each being right-handed and 
the other half left-handed. One of the lenses also is 
right-handed and the other left-handed. By this device 
the effect of double refraction is so completely neutralised 
that with a five-prism instrument it is impossible, under 
high magnifying power, to detect any duplication of the 
lines. 
The lenses are each of 52 mm. diameter and 350 mm. 
focus. The focus of the least refrangible rays is longer 
than that of the most refrangible rays, and the sensitive 
film must therefore be set at an angle to get the extreme 
rays into focus at the same time. But this alone is not 
sufficient. The focal plane is nct a flat surface, but is 
curved, and the film must therefore be curved,! and it is 
only when both these conditions are fulfilled that perfectly 
1 Chemical News, vol. xxii. p. 87, August 23, 1895; and vol. Ixxiv. 
Pp. 259, November 27, 1896. 
NO. 1553, VOL. 60] 
sharp images of spectral lines extending from the red to 
the high zinc line 2138*30 can be photographed on the 
same surface. Celluloid films are used, glass not being 
sufficiently flexible. 
Using the middle position showing the whole spectrum 
on a plate, the angle is 4o°",and the curvature is I90 mm. 
radius. 
The condensers are of quartz, and are plano-cylindrical 
—one being double the focus of the other. The object 
of this, when spark-spectra are being photographed, is 
to concentrate on the slit a line instead of a point of 
light, as would be the case if ordinary lenses were used. 
When photographing phosphorescent spectra—or, in 
fact, any spectra the wave-lengths of which are either 
unknown or require verification—I always photograph 
on the same film a standard spectrum, usually of an alloy 
of equal molecular weights of zinc, cadmium, tin and 
mercury. This forms a hard, somewhat malleable alloy, 
giving throughout the whole photographic region lines 
the wave-lengths of which are well known. The chief 
objection to this alloy is its volatility, the poles requiring 
frequent adjustment. Recently I have used pure iron for 
this purpose ; this has the advantages of giving a great 
number of fine lines whose wave-lengths are accurately 
known, and not being very volatile, the poles do not 
rapidly wear away. If the poles are kept about 1 mm. 
apart, there is little or no interference from air lines. 
The most simple method of applying the standard 
lines to an unknown spectrum is by the successive em- 
ployment of two slightly overlapping diaphragms im- 
mediately behind the slit, one being used for the experi- 
mental and the other for the standard spectrum. In 
this way, without disturbing the instrument, the two 
spectra can be recorded on the plate one over the other; 
the overlap of 1 mm. being in the optical centre of the 
train. The resulting negative is then transferred to a 
micrometer measuring machine of special construction, 
having a screw of 1/1ooth of an inch pitch, and a means 
of accurately determining 1/1oooth of its revolution, 
thus measuring directly to the 1oo/1oooth of an inch. 
In this way, in a five-prism spectrograph having lenses 
700 mm. focus, it is possible to determine wave-lengths 
of photographed lines to the sixth figure. 
MATHEMATICS OF THE SPINNING-TOP2 
Me 
& Eo those who study the progress of exact science, the 
common spinning-top is a symbol of the labours 
and the perplexities of men who had successfully threaded 
the mazes of the planetary motions. The mathematicians 
of the last century, searching through nature for 
problems worthy of their analysis, found in the toy of 
their youth ample occupation for their highest mathe- 
matical powers. 
“No illustration of astronomical precession can be de- 
vised more perfect than that presented by a properly 
balanced top, but yet the motion of rotation has in- 
tricacies far exceeding those of the theory of precession. 
“ Accordingly we find Euler and D’Alembert devoting 
their talent and their patience to the establishment of the 
laws of the rotation of solid bodies. Lagrange has in- 
corporated his own analysis of the problem with his 
general treatment of mechanics; and since his time 
Poinsot has brought the subject under the power of a 
more searching analysis than that of the calculus, in 
which ideas take the place of symbols, and intelligible 
propositions supersede equations” (Maxwell—“ Collected 
Works,” I. p. 248). 
Newton also cites the top as affording an experimental 
verification of his First Law of Motion—Lex. I. “... 
1‘*Ueber die Theorie des Kreisels.” F. Klein und A. Sommerfeld 
Heft i, ii. Pp. 196 and 197 to 512. (Leipzig: Teubner, 1897-8.) 
