Jury 13, 1899] 
on each rod, the single ring (Fig. 1) being left in contact with 
the disc, and a very small amount of paraffin wax is melted 
round the rings. When the vessel is supported with the rods 
downwards, as in Fig. 2, the solid wax holds the indexes in 
position. The arrangement is then placed between the con- 
denser and the focussing lens of the lantern, and boiling water 
is poured into the brass vessel. When that part of a metal rod, 
in the neighbourhood of the double ring of the index, reaches the 
' 
Fic. 1.—Enlarged view of index. 
melting temperature of the wax, the index commences to slip 
downwards, carrying the wax with it, and when the temper- 
atures of the rods have acquired steady values, the indexes will 
have descended to points on the various rods where the wax 
just solidifies, and which, therefore, possess equal temperatures. 
Hence, the conductivities of the various rods are proportional to 
the squares of the distances from the bottom of the brass vessel 
to the respective positions indicated by the several arrow-heads. 
Fic. 2.—Lecture apparatus for demonstrating the relative thermal con- 
ductivities of metals. (The left-hand rod is of copper, the middle one 
of brass, and the right-hand one of soft steel.) 
Ascale of equal parts, or, better still, a scaleof squares, may 
be drawn on the screen, when the relative conductivities may be 
directly read off. 
In Fig. 2, rods of copper, brass and soft steel are shown with 
the indexes in the positions acquired at the end of an experi- 
ment. It will be seen that the relative conductivities work out 
to within three or four per cent. of the accepted values for the 
mean conductivities between o° and 100° C, 
Royal College of Science, July 8. Epwin Epser. 
The Electrical Resistance of the Blood. 
Ir is no easy task to measure the electrical resistance 
of the blood of a living individual. The principal difficulty 
depends upon the fact that only very small quantities of blood 
can generally be obtained at a time. During the last five years 
many attempts have been made by me to obtain trustworthy and 
consistent results ; various methods and forms of apparatus have 
been employed and subsequently rejected. 
The best results were obtained by placing five cubic milli- 
NO. 1550, VOL. 60] 
NATURE 
245 
metres of freshly-drawn blood between two cup-shaped elec- 
trodes three millimetres in diameter, coated with spongy 
platinum, and fixed at 0°75 mm. apart. 
The average resistance of normal blood at 60° F. measured 
by Kohlrausch’s method in this apparatus is 550 ohms. A 
striking, change may be observed in pernicious anzemia, the 
resistance in this disease being sometimes diminished to about 
one-half that of normal blood. The deduction is that the blood 
in pernicious anzemia contains an abnormal amount of salts, due 
to the destructive metabolism going on. 
Dawson TURNER. 
School Laboratory Plans, 
I HAVE long believed that by far the best arrangements of 
the benches in a laboratory for elementary chemical teaching is 
the last one suggested by Mr. Richardson, viz. ‘‘ single benches, 
cross-ways, like the desks of an ordinary class room.” 
It must be remembered that qualitative analysis now occupies 
a secondary place in an elementary course, and a great number 
of reagents is not required for preparations and simple quantita- 
tive experiments. The superstructure of shelving may there- 
fore be replaced by a single rack for the common reagents. 
This allows perfect supervision from the raised demonstration 
table in front of the benches, and the work of the class can at 
any moment be interrupted for explanation or revision of the 
work done, or for an experiment made by the master himself. 
It is surely a mistake to divide an elementary course of chemistry 
into two parts—theoretical and practical ; the proposed arrange- 
ment allows of the practical work forming a part of the general 
course. 
In this county this arrangement has beer successfully carried 
out. The grammar schools are, however, unwilling to risk the 
refusal of the Science and Art Department to recognise such a 
laboratory for earning grants, the old-fashioned benches with 
uncleanly teak tops and rarely used drawers and cupboards 
being usually insisted on. T. S. DyMonp. 
County Technical Laboratories, Chelmsford. 
The Origin of the Doctrine of Compensation of Errors 
in the Infinitesimal Calculus. 
I sHOULD be much obliged if you could help me by inserting 
a query on this point. 
Lazare Carnot, at the end of his ‘‘ Reflexions sur la Méta- 
physique du Calcul Infinitésimal,’’ stated that ‘‘it is singular 
that in this indispensable condition of elimination the real 
character of Infinitesimal Quantities . . . should not hitherto 
have been discovered.” 
However, Lagrange (see ‘‘CEuvres,” t. vii. p. 595) had explicitly 
stated this doctrine many years before. Very possibly Carnot 
did not see this note, but Lagrange again stated it in the preface 
of his “* Théorie des Fonctions Analytiques,” which Carnot had 
certainly seen, as he quoted some passages from it in the later 
editions, at least, of his ‘* Reflexions.” 
If Carnot has any right toan independent discovery, he could 
hardly have quoted Lagrange in the first edition of his work. 
The first edition of both Carnot’s and Lagrange’s works was 
dated 1797. 
I have been unable to find a first edition of ‘‘Carnot”’ here, so 
write to ask if any one can tell me whether there is any mention 
or quotation of Lagrange in it. Puitir E, B. JOURDAIN. 
63 Chesterton Road, Cambridge, June 30. 
Robert Browning and Meteorology. 
RoBeRT BROWNING’s well-known description of Aurora 
Borealis, in ‘‘ Easter Day ” (c. xv. xvii), is so graphic that it must 
have been written from personal observation. Probably few 
persons can fully appreciate its accuracy ; but on September 24, 
in that wonderful Aurora year 1870, just such a display took 
place, which I had the fortunate opportunity of watching nearly 
all night from the Welsh hills, when all the phenomena 
Browning describes, and many others, were abundantly visible. 
But I can find no account of any such display having been seen 
in these latitudes earlier in the century, and ‘‘ Easter Day” 
dates from 1850. 
The lunar rainbow in ‘Christmas Eve” (c. iv. and vi.), 
which “‘ rose at the base with its seven proper colours chorded,” 
