I still, however, felt it my duty to administer what consolation I could to a fellow-creature in distress; so I repeated to him (which was the truth) that I, too, occasionally failed. Then looking at my watch, and observing to my companion that these tools were not adapted to my mode of work, I reminded him that we had a pressing engagement. I then took leave of this celebrated instrument-maker, with many thanks for all he had shown me.
After such a misadventure, I thought it would be cruel to {383} invite him to meet the learned professors who would be assembled at my evening party, especially as I knew that I should be asked to show my friends a process with which he had assured me he was so familiar. The unpretending maker of thermometers and barometers did however join the party; and the kind and considerate manner in which my guests of the university and of the city treated him raised both parties in my estimation.
I will here mention another mode of treating glass, which may occasionally be found worth communicating.
Ground glass is frequently employed for transmitting light into an apartment, whilst it effectually prevents persons on the outside from seeing into the room. Rough plate-glass is now in very common use for the same purpose. In both these circumstances there is a reciprocity, for those who are within such rooms cannot see external forms.
〈ROUGH GLASS MADE TRANSPARENT.〉
It may in some cases be desirable partially to remedy this difficulty. In my own case, I cut with my diamond a small disc of window-glass, about two inches in diameter, and cemented it with Canada balsam to the rough side of my rough plate-glass. I then suspended a circular piece of card by a thread, so as to cover the circular disc. When the Canada balsam is dry, it fills up all the little inequalities of the rough glass with a transparent substance, of nearly the same refracting power; consequently, on drawing aside the suspended card, the forms of external objects become tolerably well defined.
The smooth surface of the rough plate-glass, not being perfectly flat, produces a slight distortion, which might, if it were worth while, be cured by cementing another disc of glass upon that side. In case the ground glass itself happens to be plate-glass, the image of external objects is perfect. {384}
Occasionally I met, in the course of my travels, with various things which, though not connected with my own pursuits, might yet be highly interesting to others. If the cost suited my purse, and the subject was easily carried, or the specimen of importance, I have in many instances purchased them. Such was the case with respect to that curious creature the proteus anguineus, a creature living only in the waters of dark caverns, which has eyes, but the eyelids cannot open.
〈THE CAVES OF ADELSBURG.〉
When I visited the caves of Adelsburg, in Styria, I inquired whether any of these singular creatures could be procured. I purchased all I could get, being six in number. I conveyed them in large bottles full of river water, which I changed every night. During the greater part of their journey the bottles were placed in large leathern bags lashed to the barouche seat of my calash.