I jo General Notes. [February, 



simple and inexpensive a contrivance to their patrons (mine cost 

 one and eightpence). 



I had looked upon the " globe condenser " as one of the relics 

 of the past, and not worthy of resuscitation, until a short time 

 ago when watching an artist engraving some fine shading on 

 wood. I was struck with the sharpness and definition of the en- 

 graved lines (about ■& inch apart). It at once occurred to me 

 that this kind of illumination would suit the microscope. I there- 

 fore borrowed it and tried it first with a }£ objective (a Ross 75 °) 

 upon Pleurosig sing oblique light from the mir- 



ror; the striae came out very distinctly. I then removed the 

 globe, and the striae vanished and required a more oblique ray to 

 render them again visible. I next tried it on Synedra robusta, 

 and resolved the striae into beads ; this I had not been able to do 

 before with this objective. I next tried it with low powers ( 1 }i 

 in., 1 in. and 2 / z objectives). I first used the f$, but forgot to 

 alter the previous position of the mirror, and consequently ob- 

 tained a " black field ;" the object I had placed upon the stage 

 was Haliomma humboldtii ; I was surprised at the beautiful effect 

 upon that form. It appeared as though illuminated by intense 

 moonlight with a slight green tinge, and delightfully cool to the 

 eye. I have since purchased a smaller globe (six inches in diam- 

 eter) than the one I tried; the liquid with which it is filled is a 

 dilute solution of sulphate of copper (about J / z ounce of saturated 

 solution to one pint of water). The mixture must be filtered if 

 ordinary water is used, the intensity of color is, however, some- 

 what a matter of taste. The distance of the globe from the 

 lamp should be about two or three inches ; from the globe to the 

 mirror about eight to twelve inches. As the height of the globe 

 cannot be altered, the necessary adjustments must be made with 



f CC) the lamp, e. g., if the mirror is at A, the lamp flame 

 < B B V must be at C ; if at C, the flame must be at A. I have 



( A A J just received a letter from a friend to whom I recom- 

 mended the illumination, in which he writes: "I am delighted 

 with the black ground illumination, which is certainly softer and 

 the definition sharper than any I have tried before. Have you 

 tried it with polarized light? I think you would be pleased with 

 it, there is such great softness of tint and such impenetrable 

 blackness of field when the prisms are crossed. — F. Kitton in Science 



Arrestation of Infusorial Life. — Three years ago I brought 

 with me to the Alps a number of flasks charged with animal 

 and vegetable infusions. The flasks had been boiled from three 

 to five minutes in London, and hermetically sealed during ebul- 

 lition. Two years ago I had sent to me to Switzerland a batch 

 of similar flasks containing other infusions. On my arrival here 

 this year 120 of these flasks lay upon the shelves in my little 

 library. Though eminently putrescible, the animal and vegetable 



