would be equal to 13°752 English inches, or 1146 
, and to 34’919 centimetres, The weight of water 
oniained in such a culit foot would be 42°578 kilo- 
mmes, thus closely approximating to the weight of the 
Alexandrian Talent in the time of the Ptolemies. 
hese investigations show that it is quite possible that 
granite ball now found may have been an ancient 
gyptian Minaweight. It has been suggested that it may 
e been used as a hammer, as it is known that at early 
periods stone balls were so used ; and indeed, a part of the 
surface of the bail looks as if some of the granite had been 
mnocked away. But even if so used, it by no means fol- 
lows that it was not originally intended as a weight, for 
evidence was given before the Standard Commission by 
our Local Inspectors of Weights and Measures that brass 
Standard weights not unfrequently show evident marks 
having been used as hammers. If a portion of the 
ght had thus been knocked off, the difference between 
present weight of 539'282 grammes, and the weight of 
ancient Egyptian commercial Mina of 587 grammes, 
ht be readily accounted for. Assuming the granite 
have been really an Egyptian weight, it must be the 
t ancient weight now existing. 
Some words may be added, in conclusion, upon the 
ssibility of ascertaining the unit of ancient Egyptian 
ht from the internal dimensions of the coffer in the 
g’s Chamber of the Great Pyramid, this coffer of red 
ute having been often considered to be a standard 
sure of capacity. Its internal dimensions were accu- 
measured by Prof. Piazzi Smyth, and were deter- 
ined as follows :— 
Mean length 
» breadth ey i aes 
* »» depth 3434 » 
he capacity of the coffer is thus equal to 71°532 cubic 
ches, or 41°396 cubit feet, equivalent to 1171°129 cubic 
metres, showing its contents of water to weigh 
129 kilogrammes, equivalent to 2581°89 avoirdupois 
nds ; or, if the English weight of the cubic foot of 
r at its ordinary temperature, viz. 62°321]bs., be 
n, the contents of the water would weigh 2579'840 lbs. 
S result is in no way commensurable with the unit of 
ht derived from either of the before-mentioned ancient 
s of linear length, nor do the measurements of the 
“r agree with any round number of such units of 
h. The coffer thus fails to afford an indication to 
unit of ancient Egyptian weight, according to this 
of computation. H. W. C. 
77°93 inches 
THE DIATHERMANCY OF FLAME 
be seen by the following exposition that the criti- 
contained in the article written by W. Mattieu 
illiams, published in NATURE, vol, vi. pp.-506, 507, is 
on wrong assumptions. 
he apparatus illustrated in NaTURY, vol. vi. p. 458, 
constructed for the purpose of determining certain 
ions connected with the passage of solar rays through 
. Incidentally it admits of being employed for 
aining the retardation suffered by artificial radiant 
in passing through a series of flames. The table be- 
published contains the result of a recent preliminary 
ent instituted to show that the transparency of 
me is too imperfect to warrant the important inference 
hich Pére Secchi has drawn from Pére Provenzali’s ex- 
ment with a series of small flames. 
he assumption that the experiment published in 
JRE was intended to settle the abstract question of 
hermancy is wholly gratuitous. Probably there is no 
within the range of experimental philosophy more 
t, or requiring more time, patience, and delicate 
ments for its solution, than the diathermancy of 
sn 
NATURE 
Regarding the supposed imperfections of the apparatus 
under consideration, the following statement will suffice : 
—t. Mr. Williams asserts that the main pipe to which the 
burners are applied is too small to afford a full supply of 
gas. The internal diameter of this pipe is 0°75 ins. = 
0'4417 square ins. Now, it has been long established 
in practice that an opening of 0'0037 sq. ins. is 
capable of discharging six cubic feet of gas per hour, 
under ordinary pressure. Mr. Williams’s seventeen 
burners consumed, agreeably to his statement, /ive cubic 
feet of gas per hour. The sectional area of the 
supply pipe, imagined to be too small, is therefore ee 
= 119 times greater than the area of an opening capable 
of discharging more gas in a given time than the quantity 
consumed by the seventeen burners employed by the 
author of “The Fuel of the Sun.” 2. The assumption 
that the prolongation of the axis of the conical chamber 
passes through “ much of the blue portion of the flame ” 
is groundless. The distance of the gas-pipe from the 
conical vessel, during the experiment, was so adjusted 
that the prolongation of the axis of the latter passed 
through the flames at the point of greatest intensity. But, 
had this adjustment been neglected, the radiant heat, 
acting on the thermometer, would not have suffered any 
diminution, since the intensity transmitted depends solely 
on the extent of the ignited portion of the flame. The 
criticism regarding the position of the axis of the instru- 
ment has therefore no bearing on the question at issue. 
3. Mr. Williams’s disquisition relating to the retarding 
influence of the vapour contained in flames, so far from 
establishing the perfect diathermancy assumed by Pére 
Secchi, proves, if we admit the soundness of the reason- 
ing, that radiant heat does not pass freely through flames 
when arranged in the manner adopted by Pére Proven- 
zali. It will be well to observe that the plan of igniting 
one flame at a time in order to ascertain the radiant power 
transmitted by each was resorted to with a view of decid- 
ing the question by a similar method to that adopted by 
the Italian physicists. 
The apparatus contrived by Mr. Williams for deter- 
mining the diathermancy of flame, as described by him- 
self, is exceedingly faulty, the temperature it records being 
that produced by heat received from several sources. The 
radiant heat transmitted to the bulb of the thermometer 
by the flames, acting conjointly with the unknown degree 
of heat imparted by the surrounding medium, it will be 
evident that Mr. Williams’s device is worthless as an in- 
dicator of radiant intensity. His thermometer, agreeably 
to the published table, indicated 19° C. when exposed to a 
single flame, and 53° C. when all the flames were ignited ; 
but no information is afforded regarding the temperature 
of the enclosure (an imperfectly polished vessel) nor was 
the temperature of the air surrounding the bulb of the 
thermometer ascertained during the experiment. It is 
scarcely necessary to explain that in the absence of any 
indication of the temperature of the air surrounding the 
bulb of the thermometer, and the temperature of the vessel 
which radiates towards the bulb, the radiant intensity 
transmitted by the several flames cannot be determined. 
Again, Mr. Williams’s table, as before stated, shows that 
the thermometer indicated 19° C. under the effect of the 
radiation of ove flame, but this temperature being the joint 
result of heat radiated towards the bulb by the enclosure, 
and heat communicated by convection of the air surround- 
ing it, together with the radiant heat transmitted by the 
flame, the temperature due to the radiation of the latter, 
viz., the true radiant intensity, cannot be established. 
Experimenters possessing necessary experience are aware 
that a thermometer of proper form exposed to radiant 
heat of moderate intensity requires from twenty to twenty- 
five minutes before the mercurial column becomes so 
nearly stationary that the indication may be safvly re- 
corded ; hence, owing tothe close proximity 0 the flames, 
