The following is a new, useful, and ready method of making globules for microscopes, differing from the customary one described in page 8, and is extracted from Mr. W. Nicholson’s scientifical Journal of Natural Philosophy, Chemistry, and the Arts. No. 3, June 1, 1797. p. 134.

“The usual method has been to draw out a fine thread of the soft white glass called crystal, and to convert the extremity of this into a spherule by melting it at the flame of a candle. But this glass contains lead, which is disposed to become opake by partial reduction, unless the management be very carefully attended to. I find that the hard glass used for windows seldom fails to afford excellent spherules. This glass is of a clear bright green colour when seen edgeways. A thin piece was cut from the edge of a pane of glass less than one-tenth of an inch broad. This was held perpendicularly by the upper end, and the flame of a candle was directed upon it by the blow-pipe at the distance of about an inch from the lower end. The glass became soft, and the lower piece descended by its own weight to the distance of about two feet, where it remained suspended by a thin thread of glass about one five-hundredth of an inch in diameter. A part of this thread was applied endways to the lower blue part of the flame of the candle without the use of the blow-pipe. The extremity immediately became white-hot, and formed a globule. The glass was then gradually and regularly thrust towards the flame, but never into it, until the globule was sufficiently large. A number of these were made, and being afterwards examined by viewing their focal images with a deeper magnifier, proved very bright, perfect, and round.”

The opake solar microscope has been made by the late Mr. Martin of larger dimensions than described in page 106. The illuminating lens, at A B, Plate V. Fig. 1, and the breadth of the mirror were about four inches and an half, instead of three inches, which gives more than double the light of the former; and, consequently, all the larger sort of opake and transparent objects, to the size of one and an half or two inches in diameter, as well as diverting objects painted on glass, like the magic lanthorn sliders, are shewn with the greatest distinctness, and has by Mr. Martin been called the MEGALASCOPE of the apparatus.

The same ingenious and learned artist applied a lattice of small squares about one-tenth of an inch, each square made of fine wire, or lines drawn strongly on glass in a circle of one inch in diameter, and placed these in the compound body of a microscope or telescope, in the focus of the glasses next to the eye. And having a copper-plate lattice of squares disposed into a circle, and to any size as may be wanted, the observer or artist may then with great facility make an exact drawing on the paper of the object observed. The same contrivance is applicable to the solar microscope. This he called the GRAPHICAL MICROSCOPE OR PERSPECTIVE.

Page 127, line 24—Any pocket telescope, the drawers of which are made to allow of a further extension than usual, may be used as a compound microscope for examining birds or insects alive, in a garden on the flowers, shrubberies, &c. from a window near to the objects. There are few pocket achromatic telescopes or perspectives, but what will define and magnify objects from about six feet to any distance from the instrument. The magnifying power is inversely as the distance of the object from the telescope, and, consequently variable in an infinite degree; on which account Mr. Martin named it the POLYDYNAMIC MICROSCOPE.