576 EHRENBERG ON THE POWER OF VISION OF THE EYE 



They plainly demonstrate an unfathomableness of oi-ganic life in the 

 direction of the smallest conceivable space ; and if the word infinity be 

 too much for what we know at present, let the word unfathomableness, 

 which I have purposely employed, avert from me the reproach of exag- 

 geration, and establish the point of view which the physical, chemical, 

 and physiological inquiries of our days, should they be rendered fruitful 

 by new powers, have to take, and what deviations they have to avoid. 



III. An attempt to form a judgement respecting the Poiver of Vision of 

 the Eye and the Ultimate Power of the Microscope. 

 I will now connect with the above paper, for its illustration and con- 

 firmation, a few considerations on the power of the human eye, and on 

 the confidence and the hopes ^ichich we may found upon microscopical 

 observations and optical instruments. Up to the present moment, so 

 far as I know, we have never been able to fix a constant measure for 

 the ultimate possible power of the microscope. M. Amici, in a letter to 

 the Baron von Zach in the year 1824, (Ferrusac, Bullet, des Sc. Ma- 

 them., p. 221,) has calculated the limit of vision according to the 

 power of the eye, and stated that a space of J^ of an inch becomes im- 

 perceptible to the naked eye at the distance of 28 feet. Lately the 

 anp-les of vision for the different colours have been calculated by M. 

 Plateau, but I have no knowledge of any result from similar observa- 

 tions having reference to the microscope. I will endeavour to lay down, 

 without any pretensions, my investigations respecting the limit of vision 

 by the microscope made in a different way ; and I shall rejoice if they 

 make an addition to this branch of our knowledge and are not wholly 

 without utility. 



In the numerous opportunities which I have had of watching persons 

 eager for knowledg*; who were desirous of acquainting themselves by 

 personal observation at my house with the wonderful structure of Ihe 

 infusoria, I found to my astonishment the difference of the power of 

 vision of individuals by far more nearly coincident than I had expected, 

 and than it is generally stated tobe. When once I had placed the delicate 

 object in the right point of vision of the instrument, or directed the 

 attention of the naked eye to a very minute object, fifteen or twenty 

 persons, to whom I often showed these things at the same time, saw 

 completely alike and with the same clearness what I myself saw : they 

 very seldom took another, and then but little different, distance of the 

 object from the eye, according to what they required. In order to be 

 quite certain that I was not deceived by the politeness or shame of those 

 who might not willingly say they had seen nothing, I have often desired 

 the observers to delineate the objects seen, or minutely to describe 

 them; by which I learnt with certainty that they saw the object exactly 

 the same and quite as distinctly as I myself had seen it, and almost 



