614 
INALTOR EF 
[APRIL 29, 1897 
to the suggestion of the Council of the London Mathematical 
Society, so far as to assent to the publication of these outlines 
with all their imperfections on their heads. 
ONE of the most important problems now attracting the 
attention of seismologists is the choice of a system of stations 
in which to carry out the seismic survey of the world. In the 
plans so far proposed, advantage would, for obvious reasons, be 
taken of the existence of astronomical observatories, care being at 
the same time exercised to obtain a nearly uniform distribution of 
stations over the earth’s surface. Prof. G. Grablovitz has re- 
cently, however, made the important suggestion that these 
stations should rather follow the distribution of voleanoes and 
the great lines of fracture of the globe. He points out that the 
majority of active volcanoes are situated close to three great 
circles, and he proposes that seismic stations should be founded 
near the six points of intersection of these circles, and near 
twelve other points symmetrically placed on the three circles. 
There are several obvious difficulties in the way of such an 
arrangement ; but it is, nevertheless, one that deserves a very 
careful consideration. 
In the Bulletin de 1 Académie Royale de Belgique, M. P. de 
Heen attacks the ordinary accepted theory of the critical point, 
according to which the horizontal portions of the isothermals of 
a substance gradually diminish to a vanishing point, and the 
extremities of these portions lie on a continuous curve whose 
tangent is horizontal at that point. M. de Heen maintains that 
the rectilinear portion of the isothermals does not vanish at the 
critical point, but that just after passing that point its direction 
gradually becomes inclined to the horizontal axis. 
IN the Monthly Weather Review for January, of the U.S. Weather 
Bureau, Mr. A. L. Rotch gives an account of the cloud observations 
being made at the Blue Hill Observatory, Massachusetts, since 
May 1, 1896, in accordance with the request of the International 
Meteorological Committee. There are three theodolite stations 
in the same straight line, at which simultaneous observations of 
height and velocity are made twice daily, when conditions 
permit. Points on the clouds are selected by telephonic com- 
munication, and, when practicable, from three to five observa- 
tions are taken on the same point, at intervals of a minute, and 
are reduced by simple trigonometrical formule. The theodolite 
measurements are supplemented by other methods, devised by 
Mr. Clayton, to determine the heights of the lower clouds, in- 
cluding the use of kites. It is found necessary to employ these 
additional methods, because the low clouds are so indefinite in 
form, or cover the sky with such a uniform veil, that it is 
impossible to measure them with theodolites or photogrammeters. 
We may confidently look for valuable results from these persistent 
and careful observations. 
THE Zeitschrift for March contains an 
interesting communication on the oldest meteorographs, for 
which we are indebted to the indefatigable bibliographical 
researches of Dr. Hellmann. It was known from  Birch’s 
“* History of the Royal Society,” that Sir Christopher Wren had 
constructed a meteorograph about the year 1660; but a com- 
plete description of the apparatus was wanting, as only a portion 
of it was shown in the plate. But Dr. Hellmann has discovered 
both a description anda sketch of the instrument in the Yournal 
des voyages de M. de Monconys (Lyon, 1665-1666). As this work is 
scarce, although a later edition of it is in the Library of the Royal 
Society (London), Dr. Hellmann quotes the passages referring to 
the meteorograph, and reproduces the sketch. The rain-gauge, 
forming part of the instrument, was the first of its kind. During 
a visit to London in 1663, Monconys obtained particulars from 
Wren of a hygrometer which he had also invented, and a 
description and sketch of this are given in the Zerfschrift. 
NO. 1435, VOL. 55] 
Meteorologische 
Wren, therefore, constructed the second condensation hygro- 
meter ; but this does not appear to be generally known, as no 
mention is made of it in Mr. Symons’s ‘‘ History of Hygro- 
meters” (Quart. Fourn. Meteor. Soc., vol. vii.). The first 
condensation hygrometer was invented by Prince Ferdinand II. 
of Tuscany, about ten years earlier. 
Tue effect of hardness on the electrical and magnetic con- 
stants of steel, with particular reference to the tempering of 
the magnetic parts of instruments, is the subject of a short 
paper, by Dr. Carl Barus, in the March number of Terrestrial 
Magnetism. The following rules, given by Dr. Barus, for the 
practical treatment of magnets, where great secular permanence 
of magnetisation is the principal desideratum, should prove of 
great service in physical laboratories and to scientific instrument 
makers. (1) Rods tempered glass-hard are not to be used as 
essential parts of magnetic instruments. (2) Having tempered 
a given steel rod in such a way as insures uniformity of glass- 
hardness throughout its length, expose it for a long time (say 
20-30 hours; in case of massive magnets even longer intervals 
of exposure are preferable) to the annealing effect of steam 
(100°). The operation may be interrupted as often as desirable. 
The magnet will then exhibit the maximum of permanent hard- 
ness for 100°. (3) Magnetise the rod—whether originally a 
magnet or not is quite immaterial—to saturation, and then expose 
it again for about five hours (in case of massive magnets even 
larger intervals of exposure are preferable) to the annealing 
effect of steam (100°). The operation may be interrupted as 
often as desirable. The magnet will then exhibit both the 
maximum of permanent magnetisation as well as the maximum 
of permanent hardness corresponding to 100°. Its degree of 
magnetic permanence against effects of temperature (less than 
100°), time, and percussion is probably the highest conveniently 
attainable. 
WORKING in the physical laboratory of the Massachusetts 
Institute of Technology, Mr. R. W. Wood has succeeded in 
producing diffraction phenomena with R6éntgen rays. The 
source of the rays was an arc-like discharge between two very 
small beads of platinum in a high vacuum. The discharge 
bulb was only about an inch in diameter, while the radiation 
(which came from an area about thesize of a pin-head) was 
strong enough to show the bones in the fore-arm. The ‘‘arc” 
appeared to be a new form of kathode discharge, and could 
only be produced under peculiar conditions. Mr. Wood used a 
tube with a platinum slit 0°11 mm. wide, mounted within the 
bulb at a distance of 2 mm. from the radiating bead. The 
second slit of variable width’ was placed at a distance of 10 cm. 
from the first,and the photographic plate at distances varying 
from 10 to 30 cm. from this. The images of the slit on the 
plate showed a distinct dark line on each edge, which could 
only be explained on the supposition that interference occurred. 
The plate was at too great a distance from the slit for such an 
effect to be produced by reflection of the rays from the edges. 
Images of fine wires showed similar phenomena. 
THe study of the origin and significance of ornamental 
devices and patterns is engaging fresh workers. In a recent 
number of G/odus (Band Ixxi. p. 197), H. Strebel discusses 
certain ornamental motives of ancient Mexico. The series of 
designs with which he is here concerned are attributes of the 
Wind-god, Quetzalcoatl. The similarity of these devices from 
the Pueblo Indians, right down to Peru, indicate that there was 
an original community of culture. 
THE directors of the Biltmore Herbarium have prepared a 
catalogue of the duplicate specimens in the collection, with the 
view of effecting exchanges. The list represents mainly plants 
indigenous to Western North Carolina, which have been care- 
