Fune 10, 1886 | 
NATURE 
Sia 
‘¢Disregarding now the systematic character of some of the 
errors, and treating them as purely casual, we get as the average 
difference between the constants as got by the machine and by 
calculation from the twenty-four hourly means 0°°065. It may 
be noticed, however, that the numbers are unusually large (and 
at the same time very decidedly systematic) in the case of the 
second cylinder of the first order 4,, for which the average is as 
much as 0°°150, the seventh of a degree. 
““Tf 6, be omitted, the average for the remaining cylinders of 
the machine is reduced to 0°'047. 
“« We see, therefore, that, with the exception perhaps of 2,, the 
constants got by the machine for the mean of the days constitut- 
ing the month are as accurate as those got by calculation, which 
requires considerably more time, inasmuch as the hourly lines 
have to be drawn on the photograms, then measured, then 
meaned, and the constants deduced from the means by a 
numerical process by no means very short.” 
The curves for the twelve years 1871 to 1882 inclusive have 
now been passed through the machine, and the results obtained 
have been carefully checked so far as the arithmetical work 
involved is concerned, upon a plan approved by the Council. 
No direct check, short of passing the curves a second time 
through the machine, can however at present be put on any 
portion of the results except as regards the means, which have 
been compared with the means calculated from the hourly 
readings obtained by measurement from the curves. The results 
of this work will be published in the Hourly Readings for 
1883, but the general results may here be stated. 
As a rule, the monthly means yielded by the harmonic analyser 
agree well within a tenth of a degree with those obtained by 
calculation from the hourly measurements of the curves ; and 
although in some exceptional cases larger differences have been 
found, amounting in rare instances to as much as half a degree, 
it is probable that generally these are less due to defects in the 
working of the instrument than to other causes. In some cases 
large breaks in the curves, due to failure of photography, &c., 
were interpolated when the curves were passed through the 
machine, but not when the means were worked out from 
measurements of the curves. Some differences rather larger 
than usual, and confined chiefly to the earliest years dealt with, 
have been ascertained to have arisen from the circumstance that 
when the curves were first measured, to obtain hourly values, 
the method of making the measurements was not the same as 
that found by subsequent experience to be the preferable; and 
also that in some cases the scale-values first used were less 
accurately determined than has since been found possible. 
In both these respects the two methods were on a par in the 
later years dealt with, and therefore the fairest comparison is 
to be had with their means. 
For 1880, the average difference of the monthly mean for all 
the seven observatories is 0°'09; for 1881 it is 0°05; and for 
1882 0°06 ; and in these three years a difference of 0°°3 between 
the analyser and calculated means occurred but once, and of 
o°-2 but five times. 
What has been said is sufficient to show that the instrument is 
completely applicable to the analysis of thermograms. 
It has also been employed on the discussion of barograms, 
and the curves for the years 1871, 1872, and 1876 have been 
passed through the machine. 
The year 1876 was selected owing to the existing facilities 
for comparing the resulting figures with those obtained by 
calculation from Mr. Eaton’s means, and the result in this case 
was equally satisfactory with that for temperature already 
mentioned. 
May 27.—‘‘Family Likeness in Eye-Colour.” 
Galton, F.R.S. 
This inquiry proved that certain laws previously shown by 
the author to govern the hereditary transmission of stature also 
governed that of eye-colour: namely, that the average ancestral 
contributions towards the heritage of any peculiarity in a child 
are from each parent 4, from each grandparent ;';, and so on; 
also that each parent and each child of any person will on the 
average possess 4 of that person’s peculiarity. The eye-colours 
were grouped into light, hazel (or dark gray), and dark ; then 
it was shown that $ of the hazel were fundamentally light, and + 
of them were dark, and they were statistically allotted between 
light and dark in that proportion. The desired test of the truth of 
the laws in question was thus reduced to a comparison between 
the calculated and observed proportion of light- and dark-eyed 
children born of ancestry whose eye-colours presented various 
By Francis 
combinations of light, hazel, and dark. The inquiry was 
confined to children of whom the eye-colours of both parents 
and of all four grandparents were known. There are six 
possible combinations of the three eye-colours in the parents, 
and fifteen in the grandparents, making a total of ninety pos- 
sible classes, but of these one-half were wholly unrepresented 
in the returns, and many others were too scantily represented to 
be of use. The remainder were discussed in six different ways : 
that is to say, in two groups, a and 2, and each group by three 
methods. Ina the families were classified and grouped accord- 
ing to their several ancestral combinations of eye-colour, but only 
those groups that consisted of twenty or more children were 
used ; there were 16 of these groups and 827 children. In é 
the families were treated separately, but only large families were 
taken, viz. those that consisted of at least six children: they 
were 78 in number. In both a and 4 separate calculations were 
made on the suppositions (1) that the parental eye-colours were 
alone known ; (2) that the grandparental were alone known ; 
(3) that the parental and the grandparental were alone known. 
The conformity between the calculated and the observed 
numbers throughout every one of the six sets of calculations was 
remarkably close, and the calculated results obtained by the 
method (3) were the best. 
**Notes on Alteration induced by Heat in Certain Vitreous 
Rocks, based on the Experiments of Douglas Herman, F.I.C., 
F.C.S., and G. F, Rodwell, late Science Master in Marlborough 
College.” By Frank Rutley, F.G.S., Lecturer on Mineralogy 
in the Royal School of Mines. Communicated by Prof. T. G, 
Bonney, B.Sc., F.R.S. 
In this paper an endeavour has been made to ascertain the 
nature of the changes which are induced in a few typical vitreous 
rocks by the action of heat only. The specimens experimented 
upon were— 
(1) The pitchstone of Corriegills, Arran. 
(2) Black obsidian from Ascension. 
(3) Black obsidian from the Yellowstone District, U.S.A, 
(4) Glassy basalt lava of Kilauea, Hawaii. 
(5) Basalt of the Giant’s Causeway, Antrim. 
The Arran pitchstone was heated for 216 hours at a temperature 
ranging from 500° to about 1100° C. The clear, greenish 
belonites of hornblende, so plentiful in the unaltered rock, were 
found to have turned to a deep rusty brown through peroxidation 
of the protoxide of iron which was present in the hornblende. 
The dusty matter mixed with clear spiculz of hornblende, which 
occurred between the belonites and shaded gradually off into the 
clear glass which immediately surrounded the belonites in the 
normal state of the rock, has segregated to some extent, a sharp 
line of demarcation now existing between the dusty matter and 
the areas of clear glass, while the spicule of hornblende have 
somewhat increased in size if not in number. No actual devitri- 
fication of the glass has resulted from the heating. 
The obsidian from Ascension showed only a banded structure 
coupled with streams of colourless microliths and a few felspar 
crystals when a section of the unaltered rock was examined 
microscopically. Two specimens of this rock were artificially 
heated, the first for the same period and at the same temperature 
as the Arran pitchstone, while the second was kept for 7o1 
hours at a temperature ranging from 850° to r100° C. 
In the first specimen the banded structure disappeared entirely, 
or almost entirely, but numerous microliths are present in the 
altered rock, in which the most remarkable change consists in 
the development of an excessively vesicular structure. 
in the second specimen a vesicular structure is also developed, 
an outer crust consisting of a very thin layer of clear brownish 
glass, followed by a nearly opaque layer composed of greenish- 
brown microliths, which shades off into a colourless glass con- 
taining similar microliths, which are probably some form of 
amphibole or pyroxene. The remainder of the specimen has 
been completely devitrified. 
The Yellowstone obsidian in its normal state shows little else 
but trichites and globulites when examined under a high power. 
Two specimens of this rock were heated: the first at from 
500° to 1100° C. for a period of 216 hours, the second from 
850° to 1100° C. for 7or hours. In the first case a remarkably 
vesicular structure has been developed ; the trichites have en- 
tirely disappeared, and small granules and crystals of magnetite 
have been formed. In the second specimen the changes are 
yery peculiar. The fragment retained its original form, but the 
surface showed minute blisters or elevations, which, when 
when cracked open, revealed a cavernous structure produced by 
