TRANSACTIONS OF THE SECTIONS. 9 
seem to have no bearing whatever of an utilitarian character. And this 
is but one of numerous proofs which the progress of knowledge is daily 
accumulating, that the most abstract, and apparently transcendent truths 
in physical science will sooner or later add their tribute to supply 
human wants and alleviate human sufferings. Nor has science per- 
formed one of the least important of her functions, when she enables 
us, either in our own case or in that of others, to dispel those anxieties 
and fears which are the necessary offspring of ignorance and error.” 
On the Line of Visible Direction along the Axis of Vision. By Sir 
Davin BrewsTER. 
In Monsieur D’Alembert’s Memoir “On Different Questions in 
Optics,” published in his “‘ Opuscules Mathématiques,” tom. i., he has 
maintained the singular opinion, that distant objects, like the fixed 
stars, when viewed directly with both eyes, are not seen in their true 
direction ; that is, neither in the direction of the rays which they send 
to the eye, nor of the line (coincident with it) drawn from the point 
of incidence in the retina through the centre of visible direction. The 
author pointed out the fallacy in D’Alembert’s reasoning, and thus 
established, in opposition to the opinion of that distinguished philoso- 
pher, the law of visible direction, which he had explained at the New- 
castle Meeting. 
A Brief Account of the Camera Obscura, and other Apparatus, used in 
making Daguerreotype Drawings. By Sir Davip BRrewsTER. 
The author exhibited a very perfect apparatus, executed for him by 
Mr. Thomas Davidson of Edinburgh, who has made some essential 
improvements on the process. Sir David also exhibited several draw- 
ings taken by Mr. Davidson with that apparatus, of various buildings 
and scenes in Edinburgh. He likewise explained to the meeting the 
method of executing Photogenic Drawings on paper, as invented by 
Mr. Fox Talbot, and exhibited to the Section a series of very beauti- 
_ ful drawings executed by Mr. Talbot himself, and presented to him 
by that distinguished philosopher. 
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On a Method of Illuminating Microscopie Objects. 
By Sir Davip Brewster. 
Considering a perfect microscope as consisting of two parts, viz. an 
_ illuminating apparatus, and a magnifying apparatus, the author stated, 
| 
that it was of more consequence that the illuminating apparatus should 
be perfect, than that the magnifying apparatus should be so; and that 
the essential part of his method consisted in this; that the rays which 
form the illuminating image or disc shall have their foci exactly on the 
