1872.] Light. 399 
very close to the back combination of the objective ; this change of position, 
and also the reduction of the amount of glass traversed by the divided 
pencils, materially improves the definition of the instrument, which can now 
be used satisfactorily with a power of ith of aninch. The dimensions of the 
prisms are 0°68 of an inch in length, 0-412 of an inch in width, and 0-2 of an 
inch in thickness, and are inclined to each other at an angle of 43°; this 
makes the angle between the bodies g}°, and the imaginary point to which 
they converge nearly 15 inches. Provision is made for the employment of 
polarised light by substituting for the upper prism a plate of black glass so 
placed that the light is reflected from its surface at the polarising angle of 563°; 
a suitable alteration in the inclination of the bodies is made with this view 
without in any way affecting the use of the microscope for ordinary observations. 
This arrangement is found to give much better definition than a Nicol prism 
placed within the body. 
Captain Hutton gives, in the ‘‘ Monthly Microscopical Journal” for May, 
an account of his examination of three kinds of vegetable fibres: those of 
Phormium tenax, ‘‘ New Zealand Flax,” and ‘ Sizal” and ‘‘ Manilla Hemp.” 
He remarks, as most persons do who have studied the subje& of vegetable 
fibres, that there is no difficulty in distinguishing these substances when in 
quantity; but that character is lost when only a small amount is available 
for examination. The following results of microscopical observations are 
given :—Manilla. Fibrous bundles oval, nearly opaque, and surrounded by a 
considerable quantity of dried up cellular tissue, composed of re@angular 
cells. The bundles are smooth; very few partly-detached ultimate fibres are 
seen, and no spiral tissue. Sizal. Fibrous bundles oval and surrounded by 
cellular tissue. Smooth and very few ultimate fibres projecting from the 
bundles. More translucent than Manilla, and can always be recognised by 
the large quantity of spiral fibres mixed up in the bundles. New Zealand 
Flax (Phormium tenax). In machine-dressed Phoymium the bundles are 
translucent and irregularly covered with tissue. Spiral fibres can be detected 
among the bundles, but not in the same quantity that is seen in Sizal. Many 
more ultimate fibres stick out from the bundles, which are flat instead of oval. 
In those places where the bundles are entirely freed from tissue they are 
generally divided longitudinally into two or more smaller bundles or fasciculi, 
and in these places the number of half-detached ultimate fibres is greatly 
increased; these are, however, rarely broken, most of them having the end 
perfe&. Spiral fibres are here absent. In Maori-prepared Phormium the 
bundles are almost entirely free from tissue, and quite so from spiral fibres. 
They are always broken up into many fasciculi, which average, perhaps, some 
twelve or fifteen ultimate fibres in each fasciculus. Many ultimate fibres are 
semi-detached, and they are much more broken than in machine-prepared 
fibre. For examination of the ultimate fibre Captain Hutton recommends 
boiling for two or three hours in a weak solution of potash, and separation of 
the fibres by dissection under the microscope in water. The ultimate fibres 
of Sizal will be found to separate easily, those of Phormium with more 
difficulty, while it will require great care to prevent breaking those of Manilla; 
this latter fibre will require a much longer boiling to render separation easy. 
According to Captain Hutton’s table of measurements, the average length of 
the fibre of Phormium will be found to be nearly twice that of the others; 
while the average diameter is not more than half that of Manilla, which is 
again much less than that of Sizal. The cell wall of Phormium is also much 
thinner than that of either of the other two. These researches are a 
valuable contribution to a subject the histology of which is at present very 
little known. Good and characteristic distin@ions among vegetable fibres are 
much to be desired, and the present paper is a step towards grappling with 
the great difficulties into which these researches are attended. 
Dr. John Matthews about two years back produced a simple and ingenious 
self-centreing turn-table; this proved very useful in varnishing slides, which 
were originally truly centred; its convenience for this purpose, however, rendered 
it quite useless in the case of slides which were, as in the majority of instances, 
eccentric. This defect has been remedied by adding a second plate capable 
