564 
NATURE 
[uEwl 22, mors 

sponded to so willingly by scientific men and 
societies that they overlook the necessity of 
making any recompense for work done. In the 
medical ‘services every qualified practitioner re- 
ceives rank and reasonable pay, while consultants 
are given generous retaining fees. In legal 
circles also no advice is expected without a re- 
tainer is attached to it; and in this connection we 
are interested in the announcement that ‘“ accord- 
ing to a statement made in the House of 
Commons Sir John Simon, as Attorney-General, 
drew 18,000l. as his remuneration for the past 
year.” It should be unnecessary to urge that the 
laws of nature are of as much importance as the 
laws of the land, and that as in the present crisis 
men of science can be of greater service to the 
nation than lawyers or politicians, they should 
receive at least sufhcient reward for it to enable 
them to put aside their daily work in order to 
take up national duties. There will be no lack 
of volunteer workers among scientific men, but 
the State should understand that its responsibility 
for payment on account of expert opinion is at 
least as great in the case of science as it is in 
law, medicine, and engineering. 

THE EVOLUTION OF 
GONIOMETER. 
HE goniometer—as the instrument used for 
the measurement of the interfacial angles 
of crystals is called—has gradually developed 
from a simple and crude piece of apparatus to a 
refined and somewhat complex optical instrument, 
and the measurements made with it have become 
increasingly more accurate as the form improved, 
while on the other hand the methods of inves- 
tigating the morphological characters of crystals 
have on the whole become simpler. Nicolaus 
Steno, who (in 1669) was the first to study the 
angles between the plane surfaces of crystals, 
laboriously determined them by slicing the 
crystals perpendicular to the edges bounding the 
faces in question, and outlining the sections on 
paper. The first instrument used for the purpose 
of measuring the interfacial angles is that known 
as the contact-goniometer, and was devised by 
Carangeot in 1783; it is used to this day for 
measuring large rough crystals. This type con- 
sists essentially of two arms, one movable with re- 
spect to the other, which are laid on the faces in 
question at right angles to their common edge; 
the position on a graduated scale of the end of the 
movable arm beyond the pivot gives the angle 
required. A cheap form of this type made in 
cardboard or celluloid was designed by S. L. Pen- 
field in 1900. Accuracy to single degrees of arc 
is the utmost that can under the most favourable 
conditions be expected of the contact-goniometer. 
To the ingenuity of W. H. Wollaston, in 1809, 
is due the reflective form of goniometer. In this 
type the common edge of the pair of faces under 
measurement is set in line with the axis of a 
rotatable graduated circle, and the position of 
the circle is read when some distant signal is 
reflected by the particular face in a predetermined 
NO. 2386, VOL. 95] 
THE 

direction; the circle is rotated, and the reading 
taken corresponding to the second face. The 
difference betwen the pair of readings gives the 
interfacial angle required. In the original form 
the graduated circle was vertical, and no means 
existed for fixing accurately the direction of re- 
ference. In a goniometer described shortly 
afterwards, in 1810, by E. L. Malus, a telescope 
of low power, was used for receiving the re- 
flections, and assuring, therefore, the constancy 
of the direction of reference, and in 1839 J. 
"Babinet designed an instrument with a horizontal 
circle. E. Mitscherlich introduced many improve- 
ments and accessories in 1843; he added a colli- 
mator in place of a distant signal, and his screw 
arrangements for centring and adjusting the 
crystal are in principle the same as those generally 
used now. The horizontal-circle form of gonio- 
meter is extensively used at the present day, and 
the optical features and accessories have been 
brought to a high standard of perfection by the 
well-known firm of R. Fuess, of Berlin, who have 
devoted considerable attention to _ crystallo- 
graphical instruments. Spider-lines were first 
used in the collimator, and afterwards the ordinary 
spectroscope-slit, but neither are satisfactory for 
goniometer work owing to the diffusion of the 
image on reflection at the tiny faces such as often 
occur on crystals. The difficulty was investigated 
| by C. F. M. Websky, and in 1878 he described 
a slit, the jaws of which consisted of coplanar 
circular discs in contact, or nearly so, at the 
middle. This slit allows plenty of light to pass 
at the top and bottom, and the constriction at the 
centre admits of refined readings. In its original 
form, or slightly modified, this slit is universally 
used in modern goniometers. For the purpose of 
viewing the crystal while in position and deter- 
mining what face gives a particular reflection, the 
telescope is usually supplied with a lens which is 
applied in front of either the objective or the eye- 
piece for converting it into a microscope of low 
power. In a well-made instrument, if the crystal 
reflections admit, readings may be made to 30 
minutes of arc. 
Various modifications of this type have from 
time to time been devised. In 1903 H. A. Miers 
used an inverted form, that is one in which the 
crystal is suspended below the graduated circle, 
for making observations on crystals growing in 
their mother liquor. He also designed a stage 
goniometer for the measurement of the optic axial 
angle of small crystal flakes under the micro- 
scope. More recently, in 1911, Dr. A. Hutchin- 
son designed a convenient form of inverted gonio- 
meter for the study and measurement of tiny 
crystals or crystal fragments. In the universal 
goniometer (Fig. 1), as he terms it, the telescope 
A and collimator C are placed at some convenient 
angle to one another, and a microscope B is so 
arranged that its axis bisects the angle between 
them. The instrument may be used in the 
ordinary way as a goniometer, as an axial-angle~ 
apparatus (a fitting carrying nicol and condensing 
lens being placed for the purpose opposite the 
microscope), as a total-reflectometer of the Kohl- 
