132 



Art. XIV.— miscellaneous INTELLIGENCE. 



I. Mechanical Science. 



1. Improvements in Microscopes. — Dr. Goring has caused Mr. 

 W. Tulley, of Islington, to execute a triple acromatic lens of .333 

 inches sidereal focus, and .2 inches aperture, and another of only 

 .2 inches focus, and .11 inches aperture. Used as single lenses, 

 these constitute the utmost perfection to which magnifying glasses 

 can he brought by artificial combination, but their power is too low 

 to be extensively efficient. Applied, however, as object glasses, 

 to a compound microscope with various apertures, and eye glasses, 

 according to the nature of the body under examination, they render 

 the instrument equal to single lenses of the same amplifying power in 

 its capacity of shewing the most difficult test objects, — a degree of 

 superiority which no compound instruments in which a magnified 

 image of an object is viewed, instead of the object itself, have 

 ever yet attained * ; and in consequence of which the luxurious 

 accommodation of their large field of view, and the facilities they 

 afford for illuminating opaque objects, have hitherto been justly 

 rejected by the most distinguished naturalists in favour of the 

 simple single lens. Injustice to the celebrated Mr. Trough ton, 

 to whom science is so profoundly indebted on so many accounts, 

 it is proper to observe, that he was the person at whose suggestion 

 achromatic lenses were first made by Mr. Tulley, and which were 

 intended to be applied as the object glasses of the microscopes of 

 the Greenwich circle. The lenses in question were a little more 

 than one inch focus, and a quarter of an inch aperture, but were 

 rejected by Mr. Troughton, as no better than common ones, at 

 least for the purpose they were intended for, and with the greatest 



♦ Mr. Herschel, in a most original and masterly paper in the Transactions 

 of the Royal Society for 1 821, part 2, has ascertained the true theoretical curves 

 for giving the smallest quantity of central spherical aberration in a magnifying 

 glass composed of two lenses. Dr. Goring instigated Mr. Cornelius Varley to 

 make that combination represented at fig. 5, in the plate attached to the paper 

 alluded to, on such a scale as to give a focus of only l-6th of an inch, with 

 J-I5th inch of aperture. This forms the best object-glass for a compound 

 microscope which can be made, (excepting the achromatus,) to which it ap- 

 proximates very much in point of distinctness ; it however confuses the out- 

 line of delicate and minute transparent objects with a fringe of colour which 

 is very prejudicial to vision. As a single microscope it performs admirably, 

 and may probably be executed on a much smaller scale than l-6th inch focus, 

 so as to give a very useful power j as it \s, it shews the texture of mother-of- 

 )>earl, and the fine lines or flutings on the feathers of moths and butter- 

 flies, and other test objects which require a power three or four times higher 

 to be rendered visible in the common compound microscopes of commerce. 



