Vision 



VividiK 



SCIENTIFIC SIDE-LIGHTS 



738 



the size of my fellow men hundreds of times. 

 But the ball of a steeple and a church clock 

 are not objects of every-day experience. The 

 button of a flagstaff and the clock on the 

 wall are much more familiar. And so I 

 think of the steeple knob as the flagstaff 

 button, and the church clock as a wall clock. 

 WUNDT Psychology, lect. 2, p. 179. (Son. 

 & Co., 1896.) 



3655. VISION, NEW POSSIBILITIES 



OF Roentgen Rays Make the Opaque Trans- 

 parent. These [Roentgen] rays are pro- 

 duced by a special form of electrical current 

 sent through a vacuum tube, in or around 

 which is some fluorescent substance, which 

 under the action of the current becomes in- 

 tensely luminous. But this luminosity has 

 totally different properties from ordinary 

 light, inasmuch as the substances which 

 are opaque or transparent to it are not the 

 same as those to which we usually apply the 

 terms, but often the very contrary. Paper, 

 for instance, is so transparent that the rays 

 will pass through a book of a thousand 

 pages, or through two packs of cards, both 

 of which would be absolutely opaque to the 

 most brilliant ordinary light. Aluminum, 

 tin, and glass of the same thickness are all 

 transparent, but they keep out a portion 

 of the rays; whereas platinum and lead are 

 quite opaque. To these rays aluminum is 

 two hundred times as transparent as pla- 

 tinum. Wood, carbon, leather, and slate are 

 much more transparent to the X-rays than 

 is glass, some kinds of glass being almost 

 opaque, tho quite transparent to ordinary 

 light. WALLACE The Wonderful Century, 

 ch. 5, p. 39. (D. M. & Co., 1899.) 



3656. VISION, REMARKABLE AD- 

 JUSTMENTS FOR The Eye Surpasses the 

 Camera. As an optical instrument, the eye 

 is superior to the camera in the following, 

 among many other particulars, which may 

 be enumerated in detail: 1. The correct- 

 ness of images even in a large field of view. 



2. The simplicity and efficiency of the means 

 by which chromatic aberration is avoided. 



3. The perfect efficiency of its adaptation 

 to different distances. In the photographic 

 camera it is well known that only a com- 

 paratively small object can be accurately 

 focused. In the photograph of a large object 

 near at hand the upper and lower limits 

 are always more or less hazy, and vertical 

 lines appear curved. This is due to the fact 

 that the image produced by a convex lens 

 is really slightly curved and can only be 

 received without distortion on a slightly 

 curved concave screen, hence the distortion 

 on a flat surface of ground glass. It is 

 different with the eye, since it possesses a 

 concave background, upon which the field 

 of vision is depicted, and with which the 

 curved form of the image coincides exactly. 

 Thus the defect of the camera obscura is 

 entirely avoided, for the eye is able to em- 

 brace a large field of vision, the margins 



of which are depicted distinctly and with- 

 out distortion. If the retina had a plane 

 surface like the ground-glass plate in a 

 camera, it must necessarily be much larger 

 than is really the case if we were to see as 

 much; moreover, the central portion of the 

 field of vision alone would give a good, clear 

 picture. BERNSTEIN, quoted by BAKER in 

 Handbook of Physiology, vol. ii, ch. 19, p. 

 213. (W. W., 1885.) 



3657. VISIONS, DREADFUL, IN AL- 

 COHOLIC MANIA Reptiles and Specters 

 Seen-. Delirium Tremens. This state [de- 

 lirium tremens], which constitutes a con- 

 necting link between intoxication and in- 

 sanity, seems rather to arise from perverted 

 and imperfect nutrition of the brain than 

 from poisoning of the blood; for it may be 

 produced by other agencies which depress 

 the nervous power, such as great loss of 

 blood, the shock of severe injuries, or ex- 

 treme cold. It is characterized by a low, 

 restless activity of the cerebrum, manifest- 

 ing itself in muttering delirium, with occa- 

 sional paroxysms of greater violence; and 

 the nature of this delirium almost always 

 shows the mind of the subject of it to be 

 possessed with the apprehension of some dire- 

 ful calamity. He imagines his bed to be 

 covered with loathsome reptiles; he sees the 

 walls of his apartment covered with foul 

 or terrific specters; and he supposes the 

 friends or attendants who stand around to 

 be fiends come to drag him down into a fiery 

 abyss beneath. Here we have, as in the 

 case of false perceptions, ... a misin- 

 terpretation of actual sense-impressions, un- 

 der the influence of a dominant emotional 

 state. CARPENTER Mental Physiology, bk. 

 ii, ch. 17, p. 656. (A., 1900.) 



3658. VISIONS OF SCIENCE Con- 

 scious of Its Own Incompleteness Hopeful 

 of Mastery. From what has been said, it 

 will be seen that tho a considerable amount 

 of knowledge has been obtained respecting 

 bacteria in the soil, it may be conjectured 

 that actually there is still a great deal to 

 ascertain before the microbiology of soil 

 is in any measure complete or even intelli- 

 gent. The mere mention of tetanus and ty- 

 phoid in the soil, and their habits, nutri- 

 ment, and products therein, not to mention 

 the work of the economic bacteria, is to 

 open up to the scientific mind a vast realm 

 of possibility. It is scarcely too much to 

 say that a fuller knowledge of the part 

 which soil plays in the culture and propaga- 

 tion of bacteria may suffice to revolutionize 

 the practise of preventive medicine. Truly, 

 our knowledge at the moment is rather a 

 heterogeneous collection of isolated facts and 

 theories, some of which, at all events, re- 

 quire ample confirmation; still, there is a 

 basis for the future which promises much 

 constructive work. NEWMAN Bacteria, ch. 

 5, p. 177. (G. P. P., 1899.) 



