290 
spiders collected. When a wasp has once rchosen a site for 
building, it is very difficult to drive her away. 
63, St. George Street, Leeds Hy. Linc Rotu 
The Microscope as a Refractor 
I am rather surprised, after the judicious remarks of Dr. 
Gladstone on this subject in NATURE of July I (p. 192), to find 
Mr. Gordon Thompson still maintaining his opinion to have 
introduced anything not yet known or tried with the microscope 
adapted to this purpose. If he had had time to go over the 
papers of Royston Pigott (Proceedings of the Royal Society, 
1876), of Mr. Sorby (Afxeralogical Magazine, 1878), and of 
myself (Proceedings of the Royal Society, 1884), he could have 
convinced himself that all what he proposes has been already 
elaborated and applied. He could also have learnt why the 
method with the microscope is limited in its exactitude to the 
third decimal, as the mathematical expression which it involves 
is deduced from not very strict principles, this being as well 
the case with the formula for the hollow prism. 
The Hague, July 21 L, BLEEKRODE 
HERRMANN ABICH 
AS briefly reported in NATURE last week this venerable 
geologist died at Vienna on July 1. As far back as 
the year 1831 he began his scientific career by the publi- 
cation of an important memoir, in which by novel methods | 
of chemical analysis he determined the composition of | 
various minerals of the Spinel family, and showed how 
alike by chemical composition and crystalline form they 
could all be ranged in one group. This early paper gave 
evidence of the carefulness of observation which dis- 
tinguished him through life. It was followed by other 
chemical and mineralogical essays, especially in the de- 
partment of volcanic products. Gradually he was led to 
devote special attention to the phenomena of volcanic 
action, and in the course of his investigations to visit 
most of the volcanic districts of Europe. His folio atlas 
of views illustrative of Vesuvius and Etna (1837), and 
his “ Vulkanische Bildungen” (1841), are among the best 
known of his writings. He had great facility as a 
sketcher, and some of his drawings of volcanic craters 
have done duty for nearly half a century in text-books 
in many languages. The east of Europe presented a wide 
and almost unknown field for his exploration. As far 
back as 1840 he published notices of his wanderings in 
the Caucasus. He ascended to the summit of Mount 
Ararat, and devoted most of the remainder of his ! 
life to the investigation of the vast region of the Caucasus 
and south-eastern Europe. Many papers published from 
time to time in the scientific journals record his unwearied 
industry. But perhaps the most striking and durable 
monument of his scientific achievements is his great 
work, “ Geologische Forschungen in den Kaukasischen 
Landern,” the publication of which he was superintending 
at the time of his death. This magnificent monograph, 
of which only the first part has been published, brings 
before the reader in a series of maps, sketches, large 
panoramic views, and detailed descriptions a picture of 
the external aspect and geological structure of the Cauca- 
sian region and impresses him with a profound admira- 
tion for the author’s geological prowess. . Abich had 
during the last few years settled in Vienna, availing him- 
self of the typographic facilities to be found in the 
Austrian capital. He has been a notable instance of 
the longevity attained by many active field-geologists, for 
he almost reached the age of three score and ten years, 
retaining to the end his enthusiasm and industry. It is 
to be hoped that the second part of his monumental 
work, which is to treat of the eastern half of the Armenian 
Highlands, has been left in such a state as to admit of 
publication. ; 
NATURE 
| Fuly 29, 1886 
CAPILLARY ATTRACTION 
Il. 
OW in this second way we have, in performing the 
folding motion, allowed the water surface to become 
less by 60 square centimetres. It is easily seen that, pro- 
vided the radius of curvature in every part of the surface 
exceeds one or two hundred times the extent of distance 
to which the molecular attraction is sensible, or, as we 
may say practically, provided the radius of curvature is 
everwhere greater than 5000 micro-millimetres (that is, 
the two-hundredth of a millimetre), we should have ob- 
tained this amount of work with the same diminution of 
water-surface, however performed. Hence our result is 
that we have found 4°5/60 (or 3/40) of a centimetre-gramme 
of work per square centimetre of diminution of surface. 
This is precisely the result we should have had if the 
water had been absolutely deprived of the attractive force 
between water and water, and its whole surface had been 
coated over with an infinitely thin contractile film pos- 
sessing a uniform contractile force of 3/40 of a gramme 
weight, or 75 milligrammes, per lineal centimetre. 
It is now conveniert to keep to our ideal film, and give 
up thinking of what, according to our present capacity 
for imagining molecular action, is the more real thing— 
namely, the mutual attraction between the different por- 
tions of the liquid. But do not, I entreat you, fall into 
the paradoxical habit of thinking of the surface film as ~ 
other than an ideal way of stating the resultant effect of 
mutual attraction between the different portions of the 
fluid. Look, now, at one of the pieces of water ideally 
rigidified, or, if you please, at the two pieces put 
together to make one. Remember we are at the centre’ 
of the earth. What will take place if this piece of matter _ 
resting in the air before you suddenly ceases to be rigid ? 
Imagine it, as I have said, to be enclosed in a film every- 
where tending to contract with a force equal to 3/40 of — 
a gramme or 75 milligrammes weight per lineal centi- 
metre. This contractile film will clearly press most 
where the convexity is greatest. Avery elementary piece 
of mathematics tells us that on the rigid convex surface 
which you see, the amount of its pressure per square 
centimetre will be found by multiplying the sum ® of the — 
curvatures in two mutually-perpendicular normal sections 
1 Continued from p. 272. hs 
2 This sum for brevity I henceforth call simply ‘“‘the curvature of the 
surface”’ at any point. 
