234 
NATURE 
[May 2, r912 
determined from the observed angular deflection of the 
cube. 
with pressures ranging from o-1 to 76 cm. Hg. The 
disturbance due to radiometer action was found to 
be inversely proportional to the gas pressure, and 
could be eliminated. After allowing for the reflected 
beams, the observed torque (of the order 2x 10-° 
dyne cm.) was within 2 per cent. of that calculated 
from the energy of the beam.—Dr. T. C. Porter: 
Contributions to the study of flicker. Paper III. 
This paper is a continuation of two former papers : 
Proc. Roy.) s0C.y5voOle ix sp. 347, and) vol Vix, 
p- 313. If n be the number of revolutions per second 
for a disc with white sector ‘‘w” and the rest black, 
just to appear flickerless under illumination ‘I,’ then 
n= — 27-83 + (8-57+2-79 log I) log w (360—w) ; 
this holds when I is greater than 3-98. If I be less 
than 3-98, then 
n= —38-6+(12-4+0-77 log I) log w (360—w). 
The existence of the remarkable break in the line con- 
necting » and logI for w=180 has been confirmed. 
The relation of n and I for perfectly symmetrical 
discs of four or more sectors is established, and appli- 
cation made to the measurement of high illumina- 
tions. Asymmetrical discs are considered, and it is 
proved that » is independent of the direction of their 
rotation. With the aid of a reasonable assumption 
there is deduced a curve expressing numerically the 
rise and fall of retinal excitation with time when the 
eye has presented to it suddenly a white surface, 
which is afterwards suddenly withdrawn. This curve 
is drawn to scale for a given illumination of the white 
surface. 
Royal Microscopical Society, April 17.—Mr. H. G. 
Plimmer, F.R.S., president, in the chair.—J. D. 
Siddall; The life-history of some marine diatoms from 
Bournemouth. Living and mounted examples, draw- 
ings, photographs, and lantern slides were exhibited in 
illustration of the author’s observations, the chief 
interest of which centred in a Coscinodiscus, about 
1/400 in. in diameter, furnished with very numerous 
radiating pseudopodial filaments. The specimens 
shown demonstrated the certainty of this beyond any 
possibility of doubt, and thereby set at rest the old 
and much-debated controversy as to the possession and 
utilisation of pseudopodial appendages, at any rate in 
this particular diatom, which, for the sale of con- 
venience, he proposed should receive the specific name 
heliozoides. The presence of pseudopodial appendages, 
much smaller, fewer, and still more difficult to dis- 
cern, was also notified in Nelosira, Surirella, Bid- 
dulphia, and Triceratium. The cause of the peculiar 
movement of Bacillaria paradoxa was also _ briefly 
discussed in the paper, which concluded with the 
suggestion that further study of living diatoms with 
modern microscopical appliances would explain much 
of the meaning and purpose of the exquisite minutia 
of their siliceous skeletons.—E. B. Stringer : A modified 
form of the lever fine-adjustment, and a simple turn- 
out device for the substage condenser. The essential 
feature of the fine-adjustment was that the movement 
of the lever was carried to the top of the limb by 
means of a strong steel pin working through a guide, 
the opposing spring being at the bottom, and friction 
between the lever and the pin eliminated by means 
of a ball-bearing. Freedom from lateral movement 
and greater sensitiveness was thus secured. A simple 
two-speed movement was also provided. The turn-out 
device acted on the top lens of the condenser alone, 
thus affording illumination adapted to the power of 
the objective in use. A note was added on the value 
of the Bertrand lens in ordinary microscopical work. 
NO. 2218, VoL. 89! 
Observations were made in hydrogen and air | 
Institution of Mining and Metallurgy, 
Bedford McNeill, vice-president, in the chair.—E. 
Hatschek and A. L. Simon: Gels in relation to ore 
deposition. Actuated by the already known fact that 
dissolved substances will diffuse into and out of 
“gels,” such as gelatine and silicic acid gels, the 
authors have made a series of experiments, from 
which it appears probable that many features of the 
occurrences of gold in quartz can be explained by the 
assumption that such occurrences originated in the 
reduction of gold salts in a medium of gelatinous 
silicic acid, In these experiments the agents 
employed for the reduction of gold chloride in the 
gels were various, and comprised two groups: in 
aqueous solution—oxalic acid, ferrous sulphate, 
formic acid with ammonia, and sodium sulphite; 
gaseous—sulphur dioxide, carbon monoxide, illumin- 
ating gas, and hydrogen. The reverse process of 
adding the reducing agent to the ‘‘ gels,’ and after- 
wards pouring in the gold chloride solution, was 
also tried. The results of these experiments, as 
demonstrated in test-tubes, throw, in the authors’ 
opinion, a new light on certain gold deposits, and 
afford a more satisfactory explanation of their 
genesis than has been hitherto suggested. This is a 
matter of some importance, as the finding of alluvial 
gold has frequently led to the expenditure of vast 
sums of money in the endeavour to locate the primary 
rock source, which is possibly non-existent if these 
experiments are interpreted aright. The authors 
are making further and more exhaustive investiga- 
tions on the same lines which may lead to even more 
conclusive results.—J. I. Hoffmann: Recent practice 
in diamond drilling and borehole surveying. This 
paper may be regarded as supplementary to others on 
the same subject read previously before the institu- 
tion, and described more recent practice, including a 
detailed account of the surveying instrument now 
exclusively employed on the Rand, the invention of 
Mr. Oehman, with improvements by Mr. A. Payne- 
Gallwey. In this instrument the survey is photo- 
graphically recorded, two discs of sensitised paper 
being placed so that at a given moment they receive 
impressions from a small electric lamp, and the varia- 
tion in the image transmitted to each enables a ready 
April 18.— 
| estimation to be made of both the dip and direction 
of the borehole at the point where the record is made. 
| The paper contains folding plates giving diagram- 
matic views of two typical Rand boreholes surveyed 
by means of this instrument. A description of a 
deflecting wedge invented by Mr. Wm. Gallagher, 
used for the purpose of correcting the deviation of a 
borehole while in process of being drilled, or of 
making an offset from one already drilled, added 
interest to the paper and assisted in bringing it up to 
date.—Two other papers were on the agenda, but 
| had to be taken as read; these were:—G. T. 
Holloway: Notes on the valuation of ores and 
minerals and on _ metallurgical calculations; and 
T. A. Rickard : The domes of Nova Scotia. 
Linnean Society, April 18—Dr. D. H. _ Scott, 
F.R.S., president, in the chair.—Dr. D. H. Scott: 
Botrychioxylon paradoxum, a Paleozoic fern with 
secondary wood. The plant is from the Lower Coal- 
measures, and is a member of the family Zygo- 
pterideze, belonging to the Primofilices of Arber. 
The stele has a “mixed pith,” consisting of internal 
tracheides and parenchyma; the surrounding zone of 
wood is entirely secondary, diminishing in thickness 
upwards. The branching of the stem, as in 
Ankyropteris corrugata and some other Zygo- 
pteridez, is dichotomous. The leaf-trace, like the 
stele, shows a considerable development of secondary 
| xylem, but in the petiole the tissues of the bundle are 
