June 1, 18G6.] 



SCIENCE-GOSSIP 



135 



Toxonidea Gregoriana.— During last autumn 

 I secured several gatherings of diatoms in which 

 T. Gregoriaua were more or less present. I obtained 

 them in the outer harbour at Whitehaven a little 

 above low-tide mark. I can furnish a few slides 

 containing specimens, which I shall be glad to ex- 

 change for others of value.— B. Taylor, 57, Lowther 

 Street, 7/7/ iU Jut ecu. 



Dependency of Science.— No one who 

 attentively examines the progress of any depart- 

 ment of science, save such as are (like mathe- 

 matics or metaphysics) of a purely abstract cha- 

 racter, can fail to perceive how much it is depen- 

 dent upon the perfection of its instruments— Dr. 

 Carpenter on the Microscope" 



Fig. 134. A A. Orifices into which screw the Object-glasses. 

 B. Adapter to Microscope body. C C. Adjusting- screws 

 working through the notches x and bearing upon the stud 

 D, whereby exact lateral adjustment can be secured. 



Adjustment to Brooke's Double Nose-piece. 

 — The facility which the original nose-piece affords 

 of rapidly making use of a low or a high power, is, 

 I am afraid, not sufficiently appreciated by the 

 public; but the continuous use of one for some 

 time enables me to imagine that their limited use 

 arises from the piece of apparatus having to be espe- 

 cially adapted to the objectives. It is perhaps ne- 

 cessary to point out that the optical centre of two 

 objectives of different powers may not fall identically 

 upon the same point, not necessarily from any fault 

 in their construction, but because the smallest play 

 in the universal screw will throw it out. The instru- 

 ment itself, as all microscopists know, consists of a 

 solid bar, with two orifices, into which screw the ob- 

 ject-glasses, generally al in. and \ in., or a 2 in. and 

 f in., or \ in. and T V in. ; but where, in changing the 

 one for the other, the object looked at does not oc- 

 cupy the same position in the field, an adjustment 

 is necessary. To accomplish this two notches are 

 filed in the before-mentioned bar, into which fits a 



steel stud, against which the bar presses ; and as the 

 centre of the object-glass orifices are equidistant, the 

 only adjustment recpiired will be a lateral one, and 

 by filing out one or other or both of these notches, 

 two glasses can be centred exactly. It occurred to 

 me that, by drilling a small hole through each of the 

 notches, and fitting therein a small screw, the filing 

 might be done away with altogether, and any pair 

 of glasses adjusted with very little trouble. This has 

 been done, and the instrument (fig. 134) as altered 

 gives the greatest satisfaction. Two \ in., two \ in., 

 two i in., or even two jVin. can be readily adjusted 

 so that an object shall occupy the self-same place in 

 each. For comparison of different objectives, I 

 would point out that this piece of apparatus and 

 its adjusting screws appear to me to be very valu- 

 able, and as the alteration, or, I should say, the 

 addition, is "very inexpensive, I simply lay the 

 matter before your readers. If necessary, a fur- 

 ther adjustment could be fitted by making one of 

 the orifices moveable and sliding in a dovetail, a 

 spring being adapted to force it out; a counter- 

 acting screw would then enable any one to obtain 

 perfect centricity should the centres of the object- 

 glass orifices not be equidistant. — /. Bockett. 



Making Glass Cells. — The way to make cells 

 out of thin microscopic glass, described in Dr. Car- 

 penter's work, is well known, and after numerous 

 experiments I found that a somewhat similar 

 method could be applied to thicker glass. I pro- 

 cure two pieces of steel, or iron made hard as 

 possible, the size and shape of cell required, — in 

 short, two steel cells the pattern of the glass one 

 wanted, and about one-tenth of an inch thick. I 

 then cut some squares of ordinary window glass the 

 exact size of the steel cells; on each side of a glass 

 square I then, with marine glue, cement one of the 

 steel plates, taking care to have the edges of the 

 two steel plates and glass square all parallel ; if the 

 cementing is perfect, a hole may now be made with 

 impunity through the glass by a few taps with the 

 point of a rat-tail file, and enlarged with the file to 

 the size of the holes in the steel plates ; heat is then 

 applied to liberate the glass cell from between the 

 steel ones, a fresh square put in, and the process 

 repeated. It is obvious that cells of any size and 

 shape can be made in this manner, and by working 

 with four or five pairs of plates at once a gross of 

 cells may be made in a very short time, at a cost of 

 a few pence — a considerable saving, as glass cells are 

 rather expensive to buy. The same plan will of 

 course answer for making a hole through the centre 

 of a slide. Thin crown or plate glass is easily 

 perforated, and makes a most usefid cell. I have 

 tried to cut cells from tube with a cutting saw 

 and emery in a lathe, but the less said of this the 

 better; it can only be done with proper apparatus. 

 — E. G., Matlock. 



