This may have been the person who had the secret as well as the learned monk, because Redi states that the latter only disclosed the secret upon learning that another person had it as well as himself.

"Mr. Acland makes the following practical and valuable observations on defects of vision: -

'On the Symptoms indicating a Necessity for Spectacles.

"' The natural decay of vision occurs usually from thirty to fifty years of age, varying according to habits and employment of the individual. Some time during this interval the refractive power of the crystalline humours of the eye slightly alters its condition, whilst the crystalline lens and cornea change their form, so that a difficulty of distinct vision is felt. The eye loses a portion of its power of seeing at varying distances, or its power of adjustment; and near objects are no longer as easily seen as in youth. Reading small print by candlelight is difficult, as the book requires to be held at a greater distance from the eye than formerly, and a more powerful light is needed; and even then the letters appear misty, and to run one into the other, or seem double. And still further, in order to see more easily, the light is often placed between the book and the eye, and fatigue is soon felt, even with moderate reading.

"' When these symptoms show the eye to have altered its primitive form, spectacles are absolutely needed. Nature is calling for aid, and must have assistance, and if such is longer withheld, the eye is needlessly taxed, and the change, which at first was slight, proceeds more rapidly, until a permanent injury is produced.

"' There is a common notion that the use of spectacles should be put off as long as possible, but such is a great mistake, leading often to impaired vision for life, and is even more injurious than a too early employment.

"' Timely assistance relieves the eye, and diminishes the tendency to flattening, whereas should the use of spectacles be longer postponed, the eye changes rapidly, and when the optician is at last consulted, it is found that a deeper focus spectacle must be used than usual for the first pair, and even these suit but a short time and have to be again exchanged for those of still deeper power; and these frequent changes become a matter of necessity which, unless judiciously checked, continue during life.

"' It must not be forgotten that, when first using spectacles, they are not required during daylight, but only for reading, etc., by artificial light, and it may be from six months to two years from the time of first adopting them ere they will be required for day use.

Spectacles For The Short-Sighted

Short sight is often present at birth, but is little noticed, nor its inconveniences felt, until study becomes imperative. When this occurs, the power employed should be always slightly under that needed to remedy the defect, otherwise the eye will gradually accommodate itself to the lenses, and require constantly an increase of power. In all cases leave some little for the adjustment of the eye to do, and then you may, after a time, diminish the power of the lenses needed.

The Optician's Knowledge

Having now shown when spectacles should be employed, let us for a moment consider what are the requirements that should in all cases be possessed by the optician to whom the selection of spectacle lenses is entrusted.

"' These requirements are -

"'1st. An intimate knowledge of the anatomical structure of the eye, and of the theory of vision.

"'2nd. An extensive acquaintance with the science of optics.

"' 3rd. A sound mathematical knowledge.

"' 4th. A practical acquaintance with the manufacture of lenses and spectacle frames.

"'Having for the last fourteen years made the adaptation of spectacles my especial study, I have frequently met with cases where great injury has been done to the weak-sighted by the ordinary optician's improper selection of spectacles; and I could heartily wish more of my medical brethren would bring their knowledge to bear on this subject, - which demands, and frequently calls forth, all the science and skill we possess, to meet the requirements of some abnormal cases that present themselves'.

"The knowledge which the eye conveys to the mind is boundless; the relative condition of matter, large and small, of motion or rest, of colour, of solidity, of transparency, of brilliancy, of opacity, of space or distance, are only a few of the results attained by the exercise of the faculty of vision".