sions that I ask you to find room in your pages for this short 
protest. Epmunp P. Toy 
Middle Class Schools, Littlehampton, January 13 
A Solar Halo 
A PHENOMENON quite unusual in these parts was witnessed 
here this morning in the form of a solar halo of surpassing bril- 
liancy. The outer ring was dazzling white; the next pale lemon, 
the inner orange, and the inclosed space grayish brown, uniform 
throughout. The display was brightest at sunrise. The sky 
was clear with the exception of a few light clouds along the 
eastern horizon. The air was still. The temperature was ten 
degrees below freezing point. As the sun climbed higher the 
colours gradually faded out, until at 10,30 the last traces had 
disappeared. J. T. BROWNELL 
Mansfield, Pa., U.S.A., January.10 
Coltsfoot 
THERE is an interesting article on ‘‘Coltsfoot” in the Pad/ 
Mall for January 21, in which mention is made of fifty-two 
species of wild flowers being in bloom at Lyme Regis ; ‘‘and at 
Hastings nearly one hundred have been counted within a semi- 
circular radius of 10 miles.” Coltsfoot is amongst the flowers 
already in blossom on the south coast ; and it is instanced as a 
very remarkable proof of the mildness of this winter. I think it 
is nearly as wonderful that Corylus avellana, the common nut, 
should be in blossom on a sheltered bank in North Wiltshire. 
Not only are the catkins fully in blow, but the fertile flowers are 
also in blossom, and that not only on one, but on many bushes. 
A wood full of primroses such as we often wait for till March 
or April is another instance of absence of frost. 
, ‘T. S. MASKELYNE 
Salthrop, Wroughton, Wilts., January 23 
The Absolute Sine Electrometer 
In my paper in last week’s NATURE (p. 278), read ‘‘ 5 inch 
pitch ” instead of ‘‘y; inch pitch” for the micrometer screw. 
The diagram has been turned round counterclockwise. 
Cooper’s Hill, January 21 GrorGE M. MINCHIN 
PEDICULI.—A correspondent asks if any one can inform him 
whether in experimental researches on spontaneous generation 
pediculi have ever been the subjects of observation, and if so, 
with what results? Further, is it likely that the density of their 
dermal structures affords them a means of resistance to heat 
applied through a liquid medium ? 
PHYSICAL NOTES 
Dr. R. KO6nic has recently described a method of investiga- 
ting the nodes in the vibrating column of air in an organ-pipe. 
The pipe—a large one—is laid horizontally on its back, and a 
long slit is made the whole length of the pipe. The slit is closed 
by water, the pipe lying in a trough. A small curved tube, 
open at the end, passes down through the water and up through 
the slit into the pipe. Its other end is joined to a manometric 
capsule in conjunction with a flame apparatus of the usual type. 
The nodal surfaces can be determined to within two millimetres. 
The introduction of the tube interferes less with the conditions 
of vibration than the introduction of a tissue-paper disk or other 
explorer hitherto u ed. 
A NEw barometer, automatically recording the variations on 
an enlarged scale, has been invented by Marshall Delaey (Bud/. 
Belg. Acad., No. 8). It has the following arrangement :—The 
barometric tube, having a capacious reservoir at top, is fixedly 
suspended. The cistern is a tube slightly wider and nearly as 
long ; it bears on oue side an index, and on the other a pencil 
working on a moving cylindrical surface, and it forms the upper 
part of a kind of areometer, having a downward extension in the 
form of a closed tube floating in mercury in a wider tube, which 
communicates below, through a U-tube, with a wide and 
shallow covered cistern, the level in which is approximately 
constant. The variation of pressure is marked by the variation 
of the height of mercury in the 1e;ervoir, and this latter is to 
that of the total height in the barometric cistern (or to the path 
of the float or of the pencil) in the ratio of the section of the 
cistern to that of the reservoir (a sixth in the instrument the 
author represents), Thus an amplification is realised. 
pent dm 
THE colourless fluorspar of Switzerland, according to M. 
Cornu (Jour. de Phys., October), is a substance at least as — 
trinsparent for ultra-violet rays as quartz, and its law of disper- — 
sion is so much in harmony with that of quartz that with the — 
two a system of lenses of nearly perfect achromatism may be — 
had. ‘To give an idea of this achromatism M. Cornu states 
that he obtains on one cliché, with very satisfactory distinctness, 
the spectrum of all the photographic lines of metals, from the three — 
blue lines of zinc to the lines No, 32 of aluminium. With such © 
objectives a determination of the wave-lengths of very refrangible 
radiations becomes possible. The author describes measure- 
ments of t is kind (along with details of method) in the case of 
magnesium, cadmium, zinc, and aluminium. 6 
A RHEOMETER, for measuring currents at different depths in 
water, is described by Signor Scardona in the Rivista Scientifico- 
Industriale (September 30), It acts by pulses generated at 
intervals (according to the speed of the current) in a tube, and 
affecting a bell. The water-current acts on two screw-vanes on 
a horizontal shaft in a case attached to a vertical rod. This — 
shaft (which a flat vane keeps in a line with the current) actuates, 
at intervals, through an endless screw and a reducing system of — 
wheels, a lever applied to a caoutchouc capsule at the end of a 
metallic tube, through which, and a flexible tube attached, the — 
resulting pulses pass to the bell-arrangement (which is ina portable 
case). The rod and the metallic tube are each made up of © 
several pieces screwed together, and the vane case and tube can 
be fixed at any part of the rod. The advantages claimed over 
Amsler’s rheometer are simplicity (in dispensing with electrical 
action), and a better kind of signal (one stroke of the bell for 
each turn of a wheel). 
AN experimental inquiry by Herr Graetz (Wied. Ann. No, 10) 
into the heat-conductivity of gases and its relation to tempera- 
ture results as follows :—1. Heat-conduction in the gases air, 
hydrogen, and (with low temperatures) carbonic acid, consists in 
transference of progressive energy only ; intramolecular energy 
contributes immeasurably little. The molecules thus behave like 
material points. 2. The relation of heat conduction to tempera- 
ture is found by experiment to be such (approximately) as 
Clausius’ theory requires. 3. Alb results for gases and vapours, 
showing divergences from the values calculated from theory, are 
without evidential force, for they only gave the apparent heat- 
conducting power, in consequence of absorption of radiant heat. 
4. The divergence of the temperature-coefficient of friction from 
that calculated from theory cannot have for cause (or not alone) 
the decrease of the molecular diameter with rising temperature ; 
some other explanation must be sought. 
A USEFUL comparison of the numerous determinations of the 
expansion of water by heat is made by Herr Volkmann in a 
paper contributed to KG6nigsberg Institute (Wied. Ann. No, 
10). Experimenters, it is known, have used two methods—the 
hydrostatic and the dilatometric. The author gives in a table 
the average values for volume and density of water (deduced 
from the observations of Hagen, Matthiessen, Pierre, Kopp, and 
Jolly) for all temperatures from zero to 25°; also the volumes 
every 5° from 25° up to 100°. The temperature of greatest 
density of water is, according to the best data, +3°94° C. Herr 
Volkmann thinks there is no occasion to study the subject anew 
on the lines hitherto adopted; but it might be well (in his 
opinion) to observe the absolute expansion of water in the same 
way as Regnault determined that of mercury (with communicating 
tubes). 
IN view of assertions that the band-spectrum attributed to 
hydrogen by Herr Wiillner is really that of a hydrocarbon— 
acetylene according to Herr Ciamician—the former physicist has 
made a careful examination of the acetylene spectrum (Wied. 
Ann, No. 10), and finds that, as might be expected from the 
higher proportion of carbon in acetylene, its spectrum differs 
from that of hydrozen much more than do the spectra of ethylene 
and marsh gas, While in these latter the characteristic carbon 
bands indicate the spectrum to be that of a carbon-containing 
gas, the whole of the red, orange, and yellow part, in the other, 
resembles much more the spectrum of carbonic acid than it does 
that of hydrogen. 
Tue physical properties of indium have been very little 
known hitherto. A recent contribution on the subject by Herr 
Erhard (Wied. Ann, No. 11) treats of some of its electric proper- 
ties. As regards resistance, he finds that indium is like some other 
metals in not coming under the often-accepted rule that pure 
; metals have a change of coefficient of resistance with tempera- 
