Half-hours with the microscope : being a popular guide to the use of the microscope as a means of amusement and instruction / illustrated from nature by Tuffen West.

  • Tuffen West
Date:
[1875?]
Catalogue details

Licence: Public Domain Mark

Credit: Half-hours with the microscope : being a popular guide to the use of the microscope as a means of amusement and instruction / illustrated from nature by Tuffen West. Source: Wellcome Collection.

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    c lenses used in its construction. The technical term for the defects alluded to, are chroinatic and spheri- cal aberration. Most persons are acquainted with the fact, that when light passes through irregular ])ieces of cut glass—as the drops of a chandelier— a variety of colours are jiroduced. These colours, when formed by a prism, produce a coloured image called the spectrum. Now, all pieces of glass with irregular surfaces produce, more or less, the colours of the spectrum when light passes through them ; and this is the case with the lenses which are used as object-glasses for Microscopes. In glasses of defective construction, every object looked at through them is coloured by the agency of this proj)erty. The greater the number of lenses used in a Micro- scope, the greater, of course, is the liability to thLs colouring. This is chromatic aberration ; and the liability to it in the earlier-made Compound Micro- scopes was so great that it destroyed the value of the instrument for purposes of ob.servation. Again, the rays of light, when passing through convex lenses, do not fall — when they form a picture — all on the same plane; and therefore, instead of forming the object as presented, pro- duce a ])icture of it that is bent and more or less deformed. This is spherical aberration, and a fault which was liable to be increased by the number of glasses, in the same way as chromatic aberration. This also occurred in Compound ^Microscopes; and the two things operated so greatly to the prejudice of this instrument, that it was seldom or never used. Gradually, however, means of inqirovemeut were discovered. These defects were rectified in tele- scopes ; and at last a solution of all the difficulties that be.set the ]>ath of the ]\Iicr<).scope-maker was afforded by the discoveries of IMr. Joseph Jack.sou