October 7, 18S7.] 



SCIENCE. 



179 



training ; what is more, they are not properly appreciated. Not 

 one man in a thousand knows the amount of harm that is done to 

 young children by placing them under the tuition of testy, irritable, 

 explosive, and neurotic teachers. B. A. Hinsdale. 



Clevel.ind, O., Oct. 3. 



Objects in Teaching. 



The value of objects in giving correct ideas was brought 

 forcibly to my mind not long since while teaching a class in natural 

 philosophy at the New York State Institution for the Blind, 

 Batavia, N.Y. 



It was my custom to place before them, the day before its uses 

 and the principles which it illustrated were to be discussed, a given 

 piece of apparatus, that, by becoming familiar with the form and 

 construction, its application might the more readily be appreciated. 

 One of the class, a young man blind from infancy, with a fondness 

 for machinery of all kinds and a quick perception of the use of such 

 as was placed before him, would frequently study the lesson in 

 advance, picturing to himself as carefully as possible the apparatus 

 described. These pictures, as he told me afterwards, were far from 

 correct. 



The thorough examination and understanding of each succeed- 

 ing object, of whatever kind, add so much to the stock of correct 

 concepts, which is valuable not only for itself, but for its aid by 

 comparison in understanding others. 



One of our most successful teachers described to her class, ran- 

 ging in age from eight to twelve, as vividly as she could without 

 naming it, a ladder. Among other things, she stated that it was 

 made of wood, had parallel sides, etc., using such terms as would 

 seem to be most readily understood, and then asked for the name 

 of the thing described. For some time no one could tell : various 

 things were mentioned, one boy suggesting ' map,' the maps for 

 the blind being cut in relief from wood, with the sides of the frame 

 parallel. 



A little girl had for the first time a bird, a stuffed specimen, 

 placed in her hands, and was much surprised to tind that it had 

 but two legs, having supposed until then that birds had four. 



Whatever may be said for or against object-teaching for seeing 

 children, that of blind children is successful proportionately as it is 

 objective. J. T. MOREY. 



Perkins Institution, South Boston, Mass., Oct. 3. 



Color-Blindness. 



In the opening article in Science last week (Sept. 30) an idea 

 was suggested, or recalled, that may be of value; and I offer it 

 in view of the possible value. I have observed for twenty years 

 or more a difference in the power of my two eyes, at times, to dis- 

 criminate in light reds when viewed at a distance of fifty feet or 

 more ; and I think this difference in the visual power of the 

 two organs depends very largely, if not altogether, on the way in 

 which the eyes are used. If I have been occupied with work that 

 called one eye into active exercise, where the mind was occupied 

 in discussing the surface or object viewed, particularly if the light 

 was variable, then I find persons appear different, according to 

 which eye is used. Not only so, but the two eyes do not focus 

 the same; the image, with the tired eye, being farther off than 

 that from the eye that is rested, and of a dull gray color. If 

 I go to a lecture under such circumstances, there appear to be 

 two lecturers, — one pale and shadowy behind ; and above, the 

 other, which seems, perhaps by contrast, to take on a brighter 

 hue. Under such circumstances, I close the tired eye, — as I have 

 come to consider it, — and give it a rest, or go out into the fields 

 and give it a feast on green. Now, may not the eyes of engineers 

 vary as to visual power in the discrimination of colors with ex- 

 cessive use ? If both eyes are exhausted and need rest, the in- 

 dividual would not be able to detect his own disability. Now, if 

 that is so, it is of importance to the public that no one should be 

 on duty for a great length of time, where the safety of any depend 

 on the discriminating power of the eyes as to colors. 



And would it not be well, in testing eyes, to note the condition 

 of the individual, — whether fresh or tired, just from work or 

 just from rest .' Geo. F. WATERS. 



Boston, Oct. 3. 



Percentage of Ash in Human Bones of Different Ages. 



Referring to Watt's ' Dictionary of Chemistry,' under the 

 article ' Bone,' we find two tables of analyses of bones, — one by 

 Von Bibra, and the other by Fremy. These two scientists do not 

 arrive at the same conclusion. Von Bibra states that " the por- 

 tion of inorganic matter in bone is smaller in youth than in age, al- 

 though no regular gradation can be observed ; " while Fremy 

 holds that " the bone of a fcetus was found to yield the same 

 quantity of ash as that of a woman of ninety-seven years of age." 

 Although the actual number of analyses made by these investigat- 

 ors was large, yet simple inspection of their tables will show that 

 very few were made of the same bone in each case ; and it is evi- 

 dent that a comparison between a femur on the one hand, and a 

 tibia on the other, could not be trustworthy. 



It occurred to me as worth while to supplement their lists ; and 

 I here present what may be considered a report of progress in that 

 direction, very much yet remaining to be done. 



The extreme difficulty of getting supplied with material the his- 

 tory of which is both certain and satisfactory renders the work ex- 

 ceedingly slow. 



The bone for examination was in every instance cut from the 

 dense portion of the shaft of the femur. No subject was taken 

 who had, so far as known, suffered from rickets or other serious 

 bone-disease, and women of recent confinement were also excluded. 

 All specimens were obtained either from living persons (amputa- 

 tions) or those recently dead. After crushing in a steel mortar, ex- 

 tracting with ether, and again crushing, the ash was determined by 

 incineration in a platinum dish. The results are in the appended 

 table. 



I think enough has been done to show that the common belief in 

 the increased brittleness of bone with advancing years being due to 

 increased percentage of inorganic salts, is without foundation. The 

 appended table indicates that after manhood is reached, no varia- 

 tion in quantity of ash takes place as the years roll on. 



" The greater brittleness of the bones in age is attributed by 



