37° 
NATURE 
[JUNE 3, 1915 

Eoanthropus, assigning this human form to the 
“latter half of the Pleistocene” and giving its 
cranial capacity as “at least 1070 c.c.” Dr. 
Smith Woodward came to the conclusion that 
Eoanthropus belongs to the older Pleistocene, and 
in his more recent reconstruction of the skull 
represents the cranial capacity as 1300—230 C.c. 
above his original estimate. 
Prof. Sollas sums up his final conclusion as 
regards human antiquity as follows: “that man, 
not only in the narrower, specific sense but also 
in the broader generic sense—Homo—is a pro- 
duct of the Pleistocene epoch, the latest child 
of time, born and cradled amongst those great 
revolutions of climate which have again and again 
so profoundly disturbed the equilibrium of the 
organic world.’’ It will be seen from this extract 
that the author favours the older opinion that 
man made his first appearance at a comparatively 
recent date. 
The Body in Health. By Prof. M. V. O’Shea 
and J. H. Kellogg. Pp. ix+ 324. (New York: 
The Macmillan Co.; London: Macmillan and 
@o:, Ltd’, 19155)) Price 3s. 6d: 
Or the making of books on elementary physiol- 
ogy and hygiene there seems to be no end, and 
the tendency to the multiplication of such manuals 
is specially marked in America. Perhaps this is 
an indication that our cousins across the sea are 
more alive to the importance of health in the well- 
being of a nation; they certainly make it a much 
more universal subject of school education than 
we do. The present volume has much to recom- 
mend it; it is clear, convincing and accurate; 
it is written in simple language and well 
illustrated; as a rule it is level-headed. The usual 
space, as in all American text-books of this kind, 
is devoted to the evil of alcohol; with that one 
has no quarrel; but tobacco also is regarded as 
nearly equally bad. The following is, for example, 
quoted with approval: “I know whereof I 
speak when I say that tobacco when habitually 
used by the young leads to a species of im- 
becility; that the juvenile smoker will lie, cheat 
and steal things he would not do had he let 
tobacco alone.’’ Extravagant superlatives of 
this nature often do more harm than good. 
Wis 1D Ee 
LETTERS TO THE EDITOR. 
[The Editor does not hold himself responsible for 
opinions expressed by his correspondents. Neither 
can he undertake to return, or to correspond with 
the writers of, rejected manuscripts intended for 
this or any other part of Nature. No notice is 
taken of anonymous communications.] 
Ultra-Violet Excitation of the D Line of Sodium. 
In a letter on this subject published in Nature, 
May 13,.1 showed that sodium vapour, stimulated by 
the second line of the principal.series at wave-length 
3303 in the ultra-violet, fluoresces with emission of 
the D line, which is the first member of the principal 
series. 
Each of these lines is a doublet. The interesting 
question arises, Supposing that stimulation were con- ; vitreous substances. 
NO. 2379, VOL. 95| 




fined to one member only of the ultra-violet doublet, 
should we get emission only of the corresponding 
member of the D line, or would both components 
of the D line be emitted? The first alternative seemed 
a priori more probable, taking into account the result 
of Wood and Dunoyer, that if sodium vapour is 
stimulated by D light, one component of the D line 
is not able to give rise to fluorescent emission of the 
other. 
I have, however, succeeded in carrying out an ex- 
periment which seems to decide fairly conclusively 
in favour of the second alternative. The zine are 
spectrum shows an ultra-violet doublet very near the 
sodium doublet. My attention was directed to this 
by reading Prof. Wood’s account of his earlier 
attempts on the problem. Direct comparison of the 
spectra showed that the zinc doublet lay inside the 
sodium doublet, but that while one of the zinc com- 
ponents was situated at about one-twentieth of an 
Angstrém from one sodium component, and thus very 
nearly in coincidence, the other zinc component was 
four times as far from its sodium neighbour, and 
well clear of it. 
A zine yacuum arc in quartz was used to illuminate 
the sodium vapour bulb, interposing the filter men- 
tioned in the former paper, for the suppression of 
visible light. With currents of three or four amperes 
nothing could be seen. Increasing the current to six 
amperes, a faint emission of D light was observed. 
It was as yet too faint for spectroscopic examination, 
but was identified by the absorption methods described 
in the former letter. At 15 amperes, the light was 
bright enough for a specially designed spectroscope, 
and showed both components of the D line in about 
equal intensity. 
The current was increased in successive tests to about 
100 amperes. These large currents were only kept 
on for two or three seconds so as to avoid destroying 
the lamp. For this short time the fluorescence was 
not inferior in intensity to the light of a moderately 
salted Bunsen flame, and the components of the D 
line were seen very bright. The intensity increases 
very rapidly with the current through the lamp. This 
is due partly, of course, to the greater brightness, 
but more to the broadening of the first zinc com- 
ponent, which makes it definitely overlap the first 
sodium component. Possibly at very large currents 
this cause may even bring the second zinc component 
on to the second sodium component, but plainly the 
first overlap must come in much sooner, for the 
interval to be bridged is four times less; and at the 
lowest current which brings out the D line brightly 
enough for examination, its components are approxi- 
mately equal. 
Wood’s failure to get any D emission is probably 
to be explained by his not having used a heavy enough 
current through the zinc lamp to secure an overlap 
of the zine and sodium lines. R. J. Srrurt. 
Imperial College of Science, South Kensington, 
May 31. 

On the Sealing of Electrical Conductors through Glass. 
At the present time there is great difficulty in 
obtaining soft glass with a comparatively high 
coefficient of expansion, suitable for sealing wires 
into glass tubes, bulbs, etc. The pre-war imported 
stocks of glass for this purpose are exhausted, and 
the recently published results of glass research com- 
mittees do not contain formulas for its manufacture. 
About three years ago, Mr. George B. Burnside, of 
the natural philosophy department of the University 
of Glasgow, discovered a method of hermetically seal- 
ing electrical conductors through glass and other 
The process is simple, and 
