considerably brighter, than it does when I look at it with my Right Eye?"

I

gave him

a" Circumspector,"* and desired him to attentively examine the size of the Pupil of each Eye while his head remained in exactly the same position-and tell me in which Eye the Pupil was largest: his answer was, "Why, in the left certainly," i. e. in the Eye least exposed to the Light.

Mr. BUTT, of Bath, informed me that he saw the Five first discovered Satellites of Saturn in an Achromatic Telescope of 44 inches focus, and 2 inches aperture — by placing a patch before that part of the field of the Telescope where Saturn appeared-and thereby enabling the Pupil to expand, and the Eye to adjust itself for discerning the fainter objects, the Satellites.

In observing Double Stars, the very minute

* The CIRCUMSPECTOR, or "Diagonal Eye-glass," is a convenient assistant to a Portrait Painter, who wishes to catch a likeness unobserved, and which is perhaps the only way of obtaining the true natural expression of a Countenance- and is also an invaluable Oracle for a fair Lady to refer to, to adjust the irresistible Artillery of her Eyes and Smiles.

Star which accompanies some large Stars, (for instance the small Star near Alpha Lyra) is visible when the large Star is out of the field - with a Telescope with which it is not discernible, while the larger Star is stimulating and shutting up the Pupil.

These very striking Facts, sufficiently establish the position laid down in the commencement of this Chapter that" cæteris paribus" the impressions on the RETINA, are vivid, in proportion to the expansion of the Pupil.

These observations led me to consider how beneficial it would be to the Eyes of Painters, Engravers, and those artists whose Eyes are irritable from great exercise, if they could be so shaded, that the Pupil might be secured from being interrupted in its adjustment. For which purpose I recommend a shade made of black silk stiffened with wire, and fixed on a Spectacle frame something like the contrivance of Tubes which are made for viewing Pictures;

See an Account of the great advantages of Spectacles with Leathern Tubes, in the 3d vol. of the Phil. Trans. for the year 1668, p. 727 and 765; and for 1684 in Vol. XIV. p. 474.

such assistance to the Sight-is surely quite as advantageous to the Artist to paint with, as it is to the Amateur to examine his Picture with.

The Eye cannot adjust itself perfectly, while it is exposed to the stimulus of surrounding Objects a defence from the intrusion of collateral rays will prevent the picture on the Retina being confused by those adventitious rays which otherwise distract it; and if only those rays are admitted into the Eye which come direct from the object under examination, it will make a much more vivid impression on the Sight, which will be sharpened and strengthened very much.

This is worthy the attention of all who wish their Eyes to enjoy the utmost sensibility that they are capable of being excited to - because,

The action of the Eye is perfect in the proportion that its adjustment is perfect-and when all its attention is concentrated on one object, the sensibility of the Sight is much increased; moreover, you will not only see better, but Vision being rendered easier, your Eyes may be employed longer, with comparatively less fatigue.

The Pupil of the Eye is larger when shaded

by a Broad Brimmed Hat-such as Coachmen wear, who probably adopted this costume from its advantage in sharpening their sight.

There is no part of the Economy of the Eyes more important, than that the object they are at work upon should be placed at exactly that distance from them at which they see with the greatest ease: - this may be easily accomplished by the assistance of A DOUBLE-RISING DESK:

and hard Students will do wisely to have a High Desk at which they can occasionally stand-instead of always sitting.

to be exerted to the utmost

should be care

ful not to offend it by too much Light, which is quite as prejudicial as too little Light.

Light enough to illuminate the object, and to make it easily and perfectly visible, is all that is wanted on this occasion, the Old Proverb, "Enough is as good as a Feast," is quite true,more, is not only unnecessary, but injurious, and will not only over-stimulate the Eye-and force the Pupil to shut itself up, but if continually so irritated, the Eye will soon become as much impaired by such over-stimulation, as the Stomach is by Dram-drinking.

I have observed in my visits to a numerously attended Reading Room - that the seats next the windows were generally filled by persons wearing Spectacles, who had no doubt accelerated the necessity for so doing by a habit of over-stimulating their Eyes with superabundant Light.

The proper way of defending the Eyes from too much Light, is by preventing all that is superfluous from entering the Room, by means of Blinds or Shutters-thus, you may admit only just such a degree of Light as you find most agreeable to your Eyes.