SCIENTIFIC SUMMARY. 
105 
How to Grind a Diamond to a Jvne Point for Micros ivriting. — This is thus 
excellently explained in a letter from Mr. Wenham to Mr. Slack, which 
appears in full in the “ Monthly Microscopical Journal.” It is briefly as 
follows : — “ A fragment of diamond was imbedded in a short piece of copper 
wire, ^th in diameter, in the way described in my paper 1 On the Construc- 
tion of Object-glasses.’ This was chucked in the bow lathe or ‘jigger,’ 
and another splinter of diamond,, similarly mounted, was held against it as 
a turning tool. Both were, I suppose, about equally ground away, and you 
could see the dust flying off ; in fact, diamonds rubbed together abrade each 
other just like two pieces of slate pencil will do. It is very easy with a 
delicate touch at last to bring the rotating diamond to a point as fine as a 
needle. This is the right thing for glass ruling, and I have no doubt that 
Nobert uses the same. In Peter’s writing machine-turned points are em- 
ployed, as these only will mark in every direction. At first he used to buy 
his turned points from the diamond workers at one guinea each, and few of 
them good even at that. I explained my way of turning the points, at 
which he succeeded at the first attempt, and ever after that made them with 
his own hands. He told me afterwards that what before cost him 21s. did 
not now cost him Is.” 
Tolies' immersion \th Object-glass. — In a letter which Mr. Slack received, 
and which he published in the “ Monthly Microscopical Journal ” for Decem- 
ber, Dr. Woodward says that the Tolies’ immersion fth, by which the 
Amphipleura pictures which he sent to the Microscopical Society were 
made, works either dry or wet, the compensation being effected simply by 
altering the distance of the front lens from the other two, by means of the 
screw collar. There is also a low-angle extra front for ordinary work. He 
finds, with the high-angle fronts, the following measurements : — 
Magnifies at 4 ft. focus ; 
Angle. Micrometer screen and 
without eye-piece. 
Dry: uncovered, 110° 225 diam. 
„ for thickest cover, 140° . . . . 250 ,, 
Immersion : uncovered, 140° .... 250 „ 
„ for thickest cover, 170° upwards . 275 „ 
With central light, and on Podura, or anatomical objects, he finds this 
objective admirable. He wishes he could speak as favourably of Mr. 
Tolies’ higher powers. They are very good indeed, but he has yet to see one 
of them which will rival the so-called — th immersion of Powell and 
Lealand. 
A Machine for Puling Glass has been devised by Mr. Stanistreet, of Liver- 
pool, and is excellently figured and described in the “ Monthly Microscopical 
Journal” for December. Mr. Slack has given a very full account of it. The 
machine is constructed for ruling lines from j^th the joooo^ °f an inch 
apart, and the inventor has added to it the means of further subdivision to 
the i - 0 o 000 th of an inch, but he has not yet been able to procure any diamond 
fine enough for ruling distinctly more than about 5,000 lines per inch. Mr. 
Wenham’s letter in the preceding paragraph was called out by this 
statement. 
How to Mount Diatoms. — Headers will study with advantage the follow- 
ing method, described by Capt. Lang, in the i: Microscopical Journal ” for 
