Many persons will recollect the first exhibition of this instrument in Bond-street, by Mr. J. T. Cooper, and Mr. Cary, succeeded by the Adelaide Gallery exhibition of scientific wonders and an oxy-hydrogen microscope. The apparatus for this purpose consists of three condensing lenses and an object glass. The objects, such as live aquatic insects, are placed in glass troughs containing water; the other objects, ferns, feathers, butterflies, algæ, &c. &c., being mounted on slides in the ordinary way with Canada balsam. (Fig. 298.) [Illustration: Fig. 298. A. The lime light. C C C. Condensers. D. The object, such as a tank of water containing live insects. E. The object glasses.] IV. _The Physioscope._ This instrument, brought out at the Polytechnic during the time that Mr. J. F. Goddard managed the optical department of the institution, always excited the greatest mirth and astonishment amongst the numerous visitors; and _habitués_ of the old place may remember the good-natured inimitable maudlin simper with which poor Mr. Tait (who was one of the living objects shown on the disc) used to drink off the glass of wine and then wink at the audience. When we say Mr. Tait used to wink, of course it is understood that he was personally invisible, and his apparition or image only appeared on the disc. The countenance is brilliantly illuminated by the oxy-hydrogen light, and being placed near the lenses, the rays are reflected from the face into the physioscope, and being properly focused, and the inversion of the image corrected, the perfect representation of the human countenance is apparent on the disc. The lenses and concave reflectors required are shown in the section of the physioscope. Messrs. Carpenter and Westley, of Regent-street, have brought the manufacture of magic lanterns to great perfection; and Mr. Collins, of the Polytechnic, constructs every kind of dissolving view apparatus, oxy-hydrogen microscopes, physioscopes, &c. (Fig. 299.) With this instrument any opaque objects (provided they reflect light properly) may be displayed to a large audience. Plaster casts appear with singular beauty and softness, whilst flowers, stuffed birds, and especially humming birds, are excellent objects for the physioscope. [Page 308] [Illustration: Fig. 299. A. One or more lime lights, throwing rays reflected by concave mirrors on to the face B, from whence they are reflected to C C, the first condensers. D D. Object glasses. This instrument is made by Mr. Collins, who has the tools for making the reflectors with correct curves. The picture of the face on the disc is covered with black spots if the reflectors are not perfect.] V. _The Camera Obscura._