540 
CONDUCTING POWER FOR HEAT OF CER- 
TAIN ROGKS* 
A collection of more than twenty specimens of rocks of the best 
marked descriptions were chosen for the purpose, and were 
cut to a uniform shape and size by Messrs. Walker, Emley, and 
Beall, of N ewcastle-on-Tyne, and a part of them were sub- 
jected to experiment. The plates are circular, 5 in. in diameter, 
and half-an-inch thick, and they are as smoothly and accurately 
ground to this uniform size as was possible in the case of some 
of the refractory substances as granite, whinstone, &c., that were 
employed. On the other hand, many more friable and softer 
rocks, as chalk, coal, marl, &c., are not included in the list of 
sample sections now collected. 
The purpose of the present paper is simply to establish from 
the experiments the general dad conducting powers of the harder 
rocks, and to corroborate in the case of a few examples that 
were numerically reduced the conclusions of a similar kind that 
were obtained by Peclet. 
The rock-plate to be tested is placed on a flat-topped tin 
boiler of its own diameter to raise its temperature on the under- 
side to the boiling-point of water, while on its upper side a 
conical flat-bottomed tin flask of spring-cold water is placed, 
and absorbs the heat transmitted through the rock section from 
its heated side. A thermometer inserted through a cork in this 
flask marks the rise of temperature and the quantity of heat 
transmitted through the rock, 
A small quantity of heat is also intercepted and absorbed by 
it which requires a part of the higher temperature on the heated 
side to introduce it into the rock, but this quantity is so small 
compared to the quantity which passes through it and enters the 
water, that it may easily be allowed for by a suitable correction. 
The flask above the rock contained about $1b. of water, and 
under the action of the steam heat below, it rose in temperature 
about 1° in 35 seconds for s/aée, and 1° F. in 38 or 40 seconds for 
different kinds of hard and close-grained rocks, as granite, ser- 
pentine, marble, and sandstone ; while the time occupied for a 
similar rise in temperature was greatest in the case of a specimen 
of black shale from the coal-measures round Newcastle, when 
the thermometer rose 1° in 48 or 50 seconds, or slower than in 
the case of slate in the proportion of about 5 : 8, 
Tn this series of trials it was easily supposed that the real tem- 
perature of the surfaces of the rock-plates was considerably dif- 
ferent from those of the metallic surfaces in contact with them ; 
and a thermo-electric pair of wires attached to cork-faces was 
now applied to test the real difference of temperatures of the two 
faces of the rocks. Two platinum wires were twisted on to the 
two ends of a piece of iron wire and were connected with the 
poles of a Thomson’s reflective galvanometer. The iron wire 
itself was bent so as to bring its two twisted ends into contact 
with the opposite faces of the rock. On testing the thermo-elec- 
tric arrangement by means of a double tin lid placed between 
its cork-faces, filled with water of different degrees of tempera- 
ture on its two sides (which were measured by thermometers 
inserted in the lids), it was found that a difference of between 3° 
and 4° F. produced a deflection of 1 division of the galvano- 
meter. 
On now taking a plate of marble out of the heating vessel and 
placing it between the thermopyles, it was found that no sensible 
heat difference was recorded by it; the rock was reversed, top 
for bottom between its poles, and the effect was still insensible, 
although the heat of the finger pressing alone on one of the wire 
junctions moved the galvanometer 3° or 4°. In order to increase 
the temperature difference the rock-plate was then brought into 
contact with the metal surfaces by means of mercury; and the 
thermometric flask itself being filled with about 10 lbs. of meroury 
instead of 4 Ib. of water, it was found that the thermometer rose 
I° in Io seconds, corresponding to a transmission of 330 heat units 
per hour through a standard plate 1 in. thick, and 1 square foot 
in surface. When taken out of its cell and transferred to the 
galvanometer, the temperature difference was now found to be 
about 7° ; giving the rate of conduction about 47 heat units per 
bout, instead of between 22 and 28 heat units as assigned by 
eclet. 
The process of lifting the rock out of its cell having undoubt- 
edly produced a loss of the heat difference before the measure- 
ment was made; a new mode was} now employed, and the 
* Paper read by A. S.Herschel, F.R.A.S., before the British Association, 
Bradford, 
' NATURE 
ee 
| Oct. 23, 1873 
wire junctions were pressed against the rock faces in situ, being 
at the same time protected from the heat of the boiler and ther- 
mometer plates facing opposite to them by thick felt wads upon 
which they were fastened to those plates. In this case a very 
different variation between the two rock-faces was now found the 
difference in the case of marble being 50° or thereabouts, while 
the passage of heat into the water thermometer flask was now 
about 264 heat units per hour, corresponding to a conducting power 
of about 5} heat units per hour. The same process was applied to 
two kinds of the black shale already described, and their con- 
ducting power was found to be much less than that of the fine- 
grained marble specimen, being at the rate of only 2 or 2} heat 
units per hour. These quantities are not more than $th or ith 
part of the values obtained by Peclet for the same kinds of rocks, 
Although time did not permit these experiments to be repeated 
with a different arrangement of the apparatus, when the sources 
of error peculiar to each of them would have been easily removed, 
as their origin in each case is easily explained, yet they confirm 
provisionally the values of the thermal conductivities found by 
Peclet ; since in two experiments which certainly gave the values 
alternately in excess and defect, the quantities obtained varied 
from 5 or 7 to 42 or 47 heat units per hour for a kind of marble 
to which Peclet assigns 22 or 28 heat units per hour as its con- 
ducting power ; and in the case of some other rocks of which 
Peclet describes the conductivity as about half that of the close- 
grained marble just mentioned, the values found by experiment 
also indicate a smaller thermal conductivity of these rocks in 
almost exactly the proportion which Peclet has assigned. - 
The form in which it will be desirable to repeat these experi- 
ments is one which will show the amount and kind of influence 
exercised by junctions between the surfaces of solid, liquid, and 
gaseous bodies in retarding the transmission of heat across them ; 
as well as to conclude the actual thermal conductivities of the 
materials employed, and for this purpose a suitable modification 
of the apparatus and of the mode of conducting the experiments 
has been contrived, which it may be expected will fully effect 
the objects which it is thus intended t o obtain. 
THE DIVERTICULUM OF THE SMALL INTES- 
TINE CONSIDERED AS A RUDIMENTARY 
STRUCTURE * 
“THE author took this structure as an illustration in reply to 
those who are not yet satisfied that structures exist which 
are useless to the animal body containing them, Referring first 
to the case of the appendix vermiformis of the great intestine, a 
survey of the anatomy of the caecum in various animals, and of 
the stages of its development in man, leads to the inference that 
this worm-like appendage is a rudimentary and virtually a useless 
structure. It has, however, been generally supposed that, being 
present, it must have some function ; and as it was manifest that 
a thing of this kind at the otherwise closed end of the great 
intestine is a source of danger by admitting foreign bodies which 
it could not expel, it has been argued that contrivances designed 
to avert this danger might be recognised. That it opens at the 
back instead of at the bottom of the cecum 3, that its opening is 
oblique ; that it has a kind of valve ; that it is directed more or 
less upwards ; and so on. On the contrary, the worm-like 
appendix is a vestige, the rudimentary representative of the true 
cecum, and all these supposed contrivances by which the danger 
is lessened are simply the result of the forward and downward 
development of the great intestine away from the resisting wall 
of the abdominal cavity against which the appendix and back of 
the intestine lie. Although from this cause the appendix vermi- 
formis is not nearly so dangerous a structure as it might have 
been, it is, notwithstanding, occasionally the cause of death. 
The author knew of several cases of this, and every experienced 
pathologist must have met with it. Foreign matters get im- 
pacted, causing ulceration, and perforation takes place, followed 
after a few hours by death. : 
The conclusion, however, that there are parts within the animal 
body which are useless, and worse than useless because dange- 
rous, is so distasteful to the adherents of the extreme theological 
school that they will rather fall back on the bare possibility of 
some unknown function even for such a rudiment. The diverti- 
culum of the small intestine may be employed here to complete 
the argument. Although in “a classification of rudimentary 
* Abstract of a paper read by Prof. Struthers, F.R.S.E., of Aberdeen, 
before the British Association, Bradford, r 
