MISCELLANY. 



6 33 



Palls 10 in a few minutes, but observations 

 show that there was no air-current from the 

 north. These sudden gusts of cold must de- 

 scend from the higher atmospheric regions. 



School Hygiene. Dr. Richard Liebreich, 

 the eminent oculist, read a paper on 

 " School Hygiene " at a recent meeting of 

 the London Social Science Association. He 

 spoke of the influence of the posture of 

 children during school-time, restricting him- 

 self to the discussion of two points, namely, 

 short-sightedness and lateral curvature of 

 the spine. Short-sightedness, he said, is 

 produced by the lengthening of the antero- 

 posterior axis of the eye, by the increased 

 tension of the apparatus with which we adapt 

 our eyes to different distances. The tension 

 is stronger in proportion as the distance is 

 shorter to which the eye is adjusted. If this 

 power is made use of for adjusting the eye 

 continually to a much shorter distance than 

 would be required ; i. e., if, in reading or 

 writing, the eyes, instead of at twelve to 

 fifteen inches, are kept at four to six inches' 

 distance from the book, the sclerotic, or 

 membrane which keeps the globe of the eye 

 in shape, giving way by degrees to the press- 

 ure, gradually extends antero-posteriorly. 

 Thus the eye becomes oval, and the retina 

 is somewhat removed from the optic media, 

 from the cornea, and the lens. The retina 

 then only receives the images of near ob- 

 jects ; distant objects appear undefined, 

 and can only be seen by the aid of concave 

 glasses. 



The abnormal posture of children during 

 school-time, and especially while writing, is 

 productive of spinal curvature. Pupils are 

 forced every day, for several hours, to main- 

 tain the same unhealthy posture, overtiring 

 always the same muscles, twisting and 

 bending the spine always at the same place, 

 and thus gradually altering the shape and 

 position of the bones. The normal position 

 would be to keep the upper part of the body 

 straight ; the shoulder-blades, both of the 

 same height, freely suspended, together with 

 the upper arm, on the ribs, and in no way 

 supporting the body ; both elbows on a level 

 with each other, and almost perpendicular 

 under the shoulder-joint, without any sup- 

 port ; only the hands and part of the fore- 

 arm resting on the table ; the weight of the 



head freely balanced on the vertebral col- 

 umn, and not on any account bent forward, 

 but only turned so much round its horizon- 

 tal axis that the face may be inclined suffi- 

 ciently to prevent the angle at which the 

 eye is fixed on the book from being too 

 pointed. 



Dr. Liebreich then presents the follow- 

 ing design for school desks. The top of 

 the desk has an inclination of 20 for writ- 

 ing ; for reading, a greater inclination is 

 required about 40. This latter is ob- 

 tained by turning up a flap of five inches 

 in width, fixed to the front edge of the 

 desk. All seats have backs, consisting 

 only of a board three inches wide, which, 

 placed at the right height, sufficiently 

 supports the lower joints of the spine, to 

 enable the pupil to keep straight while 

 reading or writing. The distance between 

 the back of the seat and the table can be 

 regulated to the size of the pupils, and is 

 always just sufficient for the flap to come 

 quite near the child when writing. 



Floating of Solid in Molten Iron. In a 



communication to the American Journal of 

 Science, Prof. Adolf Schmidt takes exception 

 to Mr. R. Mallet's explanation of the phe- 

 nomenon of certain metals in the solid state 

 floating upon a bath of the same metals in 

 a molten state. Mallet assumes the exist- 

 ence of what he terms a " repellent force." 

 Prof. Schmidt upsets this assumption by an 

 experiment which he thus describes : " Have 

 a solid ball of cast-iron of one and a half 

 to two inches diameter cast and filed off 

 pretty smoothly. Have a ladle or vessel of 

 at least three-quarter cubic foot capacity 

 filled with molten cast-iron. If, then, you 

 lay the cold cast-iron ball on the surface of 

 the molten iron, you will find that the ball, 

 in spite of the ' repellent force,' assumed 

 by Mr. Mallet, will sink to the bottom of 

 the ladle at once. With an iron rod you 

 can feel the ball at the bottom of the ladle, 

 and roll it about. But, after twenty or 

 thirty seconds, the ball will slowly rise to 

 the surface of the bath and remain there. 

 It is thus evident that cast-iron, at ordinary 

 temperatures, is both heavier and denser 

 than molten iron, but that, as its tempera- 

 ture rises, the solid iron expands, and be- 

 comes lighter, and finally floats on the mol- 



