SCIENCE. 



[Vol. XL No. 258 



The conclusions that these tables enable us to draw are, that we 

 feel a sensation of cold more quickly than one of heat, though the 

 difference is slight ; again, that we re-act more quickly to sensa- 

 tions of contact than to those of temperature. If the stimulation 

 be applied to the same spot repeatedly and at short intervals, the 

 time is in general lengthened. This was found to be true for the 

 'forehead and cheek, for sensations of cold, after a very few min- 

 ■utes. The same is true for the forehead with the stimulation by 

 'heat; but on the cheek after fifteen minutes, with the time taken 

 ■each minute, there was no such lengthening of the time. More de- 

 tails regarding the method of obtaining these results will be given 

 in a future paper. 



The same topic has also been investigated by Dr. Goldscheider 

 {Archiv fur Anat. tmd Phys., 1887, v.). His method was to ap- 

 proach a metal ball to the skin, thus breaking an electric connec- 

 tion and re-acting by a simple movement of the jaw. To get re- 

 liable results, he chose parts with a thin epidermis, and used an in- 

 tense stimulus. For cold, the ball was at a temperature of 15° C. ; 

 and for warmth, at a temperature of 5o°C. In all, over two thou- 

 sand observations were made. The average of all these times was, 

 for cold, on the face, near edge of the eyelid, .135, on upper arm 

 ,150, on the abdominal surface .226, and on the inner surface of the 

 thigh .255, of a second. Corresponding times for the perception of 

 warmth on the four places were .190, .270, .620, and .790 of a 

 second. Warmth is thus much more slowly perceived than cold, 

 ■and the more so the farther from the brain the part of the body 

 tested, the difference amounting in the lower limbs to nearly half a 

 second. It should be said that care was taken to choose parts of 

 equal sensibility in the several regions of the body. If the stimu- 

 lation is only moderately strong, and especially if the stimulation is 

 weak, the re-action time is much lengthened. For example : a 

 moderately warm stimulus on the arm takes .46 to .54 of a second 

 to be re-acted upon, and, if the stimulus is weak, it takes .90 of a 

 second to i.i seconds. That this lengthening of the time is really 

 an effect of the intensity of the stimulus, is shown by the fact that 

 lit occurs in weak stimulation of the most sensitive areas, and not 

 only in strong stimulation of insensitive areas, as would be the case 

 ■were the lengthening due to the slow radiation through the epider- 

 mis. These facts are all in good accord with former investigations 

 ■of the topic. The explanation of this difference between the re- 

 action time for heat and for cold cannot yet be given. But Dr. 

 •Goldscheider is not ready to ascribe it to the fact that the one 

 sensation passes up the white columns of the cord and the other 

 through the gray matter. The results of the two investigations 

 -agree fairly well on the time for the perception of cold, but the lat- 

 ter gives much higher values for the re-action time to a warm stim- 

 ■ulus. 



Visual Units in the Retina. — In viewing a series of uni- 

 formly scattered dots, we will at a certain distance be able to rec- 

 ognize them as dots; but if the object be further removed, they 

 will fuse into a more or less uniform surface. By testing back and 

 forth, one can quite accurately determine the distance from the eye 

 ■at which the dots are just visible as single dots, and, if we measure 

 the distance between the dots, it is possible to calculate how large 

 a surface on the retina is necessary to impress us with the vision of 

 a separate dot. Such a surface would be a visual unit, and the 

 point of importance is to find what anatomical basis there is for 

 this physiological unit. In 1881 Carl Du Bois-Reymond measured 

 the size of these visual units in the fovea, or yellow spot of the ret- 

 ina, and found that such a unit was exactly the size of a cone at 

 this point. He did not use dots, but rays of light shining through 

 holes in a screen. This makes it extremely probable that a cone is 

 the anatomical unit of vision. Dr. Wertheim (Graefe's Archiv, 

 1887) has continued these determinations for the lateral parts of the 

 retina, where the vision is less fine, and where it is in general known 

 that the number of cones is fewer. In tracing the decrease in the 

 number of visual units to a certain area as we go upwards from the 

 centre of the fovea, he gets a curve, showing at first a marked de- 

 crease, then a short period of almost no change, and then a long 

 period of slow, regular decrease. If we ask. How does this har- 

 monize with the anatomy ? the answer cannot be as definite as 

 we would wish. The part of the curve showing a marked decrease 

 corresponds to the outer parts of the yellow spot ; and the ratio 



between the number of visual units at the edge of this, compared 

 to the number in an equal surface of the centre, is as one to two or 

 three, while the ratio of the number of the cones in the two places 

 is about as one to three or four. The next period of tlie curve can- 

 not be thus compared, because the size of the yellow spot is differ- 

 ently determined by different observers. With regard to the lateral 

 portions of the retina, it can be said that the largeness of the visual 

 Units makes it necessary that the cones be separated, and this the 

 anatomy bears out. The general conclusion is, then, that the cones 

 are very probably the anatomical basis for the visual units, and that 

 the rods (that become more numerous as we recede from the cen- 

 tre of the fovea) cannot convey the sensation of a single objective 

 point. 



The Psychology of Joking. — Dr. Hughlings- Jackson pub- 

 lishes some interesting remarks on this topic in the Lancet of Oct. 

 27. He regards punning as the lowest stage of the evolution of 

 humor, but even in the pun he sees a material for the study of nor- 

 mal mentation. In a pun we have two ideas called to the mind at 

 once, — a double vision, as it were ; and, as all thought is the com- 

 parison of relations, this is simply a caricature of the normal pro- 

 cess of thought. Again : the world owes a great debt to the first 

 punster, because he began the ' play ' of the mind (in the same 

 sense as art is founded on the play-instinct), and so detached him- 

 self from the grossly useful, and showed a surplus energy capable 

 of developing into the highest traits of mankind. To lack a sense 

 of humor is a bad thing. " The man who has no sense of humor, 

 who takes things to be literally as distinct as they superficially ap- 

 pear, does not see fundamental similarities in the midst of great 

 superficial differences, overlooks the transitions between great con- 

 trasts. I do not mean because he has no sense of humor, but be- 

 cause he has not the surplus intellect which sense of humor im- 

 plies." Again : " I think that observation confirms what a priori 

 seems likely, —th^X pari passu with the evolution of the sentiment 

 of jocosity (playing at unreality) is the evolution of power of realis- 

 tic scientific conception, — from sense of the merely ridiculous with 

 parallel realistic conception of simple things, up to sense of humor 

 with parallel realistic conception of complex things." Dr. Jackson 

 then looks upon punning as a ' mental diplopia ' in which there is 

 a double mental vision, but not of the \dnA conducive to useful 

 ends. It is something like the thought in dreams. He sums up 

 his view in these words : " The process of all thought is double, 

 in degrees from a stereoscopic unity of subject and object to mani- 

 fest diplopia (two objective states in one subject). The process of 

 all thought is tracing relations of resemblance and difference, from 

 simplest perception — to say what a thing is, is to say what it is 

 like and unlike — up to most complex abstract reasoning. The 

 formula of the caricature of the normal process of thought is the 

 ' pretence ' of some resemblance between things vastly different, 

 from punning, where the pretended resemblances and real differ- 

 ences are of a simple order, up to humor, where both are highly 

 compound. We have the 'play' of mind in three degrees of evolu- 

 tion, three stages of increasingly complex incongruousnesses." 



BOOK-REVIEWS. 



Geology and Mining Industry of Leadville, Colorado. With Atlas. 

 By Samuel Franklin Emmons. (U.S. Geol. Surv., Mono- 

 graph XII.) Washington, Government. 4°. 

 The magnificent volume in which the geology of the Mosquito 

 Range, and more particularly that of the environment of Leadville, 

 Col., and its mining industry, is described, contains the results of 

 investigations begun in 1S79, at the instance of Clarence King, first 

 director of the United States Geological Survey, and continued 

 until May, 1881. Abstracts of the results of these investigations 

 have been published in the ' Second Annual Report of the Director 

 of the Survey,' but it is only now that the full work and the magnifi- 

 cent atlas have been issued. We will cull only a few points from 

 this great work which are of general interest. The first part of the 

 book deals with geology. A brief history of the discovery and 

 growth of the Leadville region is given. Emmons demonstrates 

 that the paleozoic and mesozoic strata lie unconformably on the 

 Archaean, and, what is of the greatest importance, that the forma- 

 tion which is immediately adjacent to the Archsan varies from 



