SCIENCE, 



[Vol. XVII. No. 433 



ble book "Physical Laboratory Practice" (Rivington's), has 

 advocated the use of a simple balance costing only four 

 shillings. However suitable this may be for demonstrating 

 certain principles in physics, its use is to be entirely depre- 

 cated, in my opinion, for the purpose I have in view. I 

 ■would urge most strongly that a far better instrument be 

 procured, such as one of Becker's (of Rotterdam; English 

 agents, Townson and Mercer) balances, costing, with suita- 

 ble weights, about £8. In using such a balance, care has to 

 be taken in releasing the beam and in bringing it to rest 

 again ; the pans must not be allowed to swing from side to 

 side, but must be made to move gently up and down; the 

 weights must be lifted on and off the pans with pincers, not 

 touched by the fingers, so as to preserve them untarnished; 

 and the weighing can, and in fact must, be made with con- 

 siderable exactness. Finding that so many precautions have 

 to be taken, and being severely reprimanded if careless in 

 using such a balance, the child acquires a wholesome respect 

 for the instrument, and soon becomes careful and exact. 

 Weighing with the four-shilling pair of scales can afford no 

 such discipline: their use in no way serves to correct the 

 tendency (to quote a schoolboy phrase) to "muck about," 

 unfortunately inherent in youth, — a tendency which can, I 

 believe, be more successfully counteracted by proper measure- 

 ment lessons than in any other way. The objection made to 

 the purchase of so costly a balance for school use, I hold to 

 be quite unwarrantable. Schools have no hesitation in 

 charging for the use of books, and a charge of half a crown 

 a year would more than cover their cost, if it were not pos- 

 sible to provide weighing appliances as part of the school 

 furniture. I have been told that you cannot tr-ust boys to 

 use so delicate an instrument as that I advocate: and proba- 

 bly yod cannot, if you wait until they have grown past con- 

 trol; but I believe that the difficulty will not arise if the in- 

 struction be given to children when quite young. 



Having learned to measure and weigh exactly, the children 

 may be set to examine things generally. One of the best 

 exercises that can be devised consists in weighing and meas- 

 uring rectangular blocks of different kinds of wood, and 

 then reducing the results so as to ascertain the weights of 

 equal bulks. In this way the child is led to realize that in 

 the several varieties different amounts of the wood-stuff are 

 packed in the same space; that some woods are denser than 

 others. The relative densities may then be calculated, tak- 

 ing the lightest as standard; and also their densities, i.e., 

 the quantity of wood-stuff in the unit of volume, choosing 

 several different units both of mass and of volume. The 

 data thus obtained may be made use of in many ways, e.g., 

 in setting arithmetical problems as to the weights of planks, 

 etc., of various sizes; and lessons may at the same time be 

 given as to the uses and characters of the different woods, 

 the trees from which they are obtained, etc. In a similar 

 manner, common liquids may be studied comparatively with 

 the aid of a simple "density" bottle, constructed by filing a 

 nick down the glass stopper of an ordinary two ounce nar- 

 row-mouth bottle, which may also be used in determining 

 the relative density of solids of irregular shape. Children 

 are thus put in possession through their own efforts of a 

 series of numerical data whereby various materials may be 

 characterized, and can be led to realize that it is possible to 

 convey exact information by quoting these numerical data. 



It is almost superfluous to point out that when the use 

 of the balance has been learned, a stage is reached at which 

 the study of levers and other simple mechanical powers 

 jnay very properly begin ; and that the determinations of 



densities of liquids serve as an appropriate introduction to 

 hydrostatics. 



Measurements of another kind, which afford most valua- 

 ble training, are those effected with the aid of a thermome- 

 ter. It is most important that the use of this instrument 

 should be generally understood, especially by women. It is 

 astonishing how few people know the temperature at which 

 water boils, and how mysterious an instrument to most is 

 the clinical thermometer. Practice having thus been ac- 

 quired in making measurements, and considerable knowledge 

 having been gained of properties of common materials, I 

 would advocate the quantitative study, especially by girls, 

 of the effect of heat on vegetable and animal food materials, 

 and subsequently on earthy substances and metals. Such 

 exercises would serve as an appropriate introduction to the 

 study of chemical change, which at this stage should be en- 

 tered on more particularly with the ob.iect of developing the 

 reasoning powers. I propose to give two examples by way 

 of illustration. The one relates to the discovery of the com- 

 position of air; the other, to the discovery of the compositioni 

 of chalk. 



In considering air, it is the practice with most teachers, I 

 believe, to explain, and in some cases demonstrate, how 

 oxygen may be prepared, and how brilliantly many sub- 

 stances burn in it; air is then stated to be a mixture of oxy- 

 gen with nitrogen in certain proportions, and certain proofs 

 of this statement are advanced. Although much interested 

 in the statements, and delighted at witnessing the flrework 

 displays which attend combustion in oxygen, the young stu- 

 dent is not much the wiser for such lessons: a certain 

 amount of "prepared food " has been put into his or her 

 mouth, but no understanding acquired as to how it has been 

 prepared, or whence it came. I advocate an entirely differ- 

 ent course: I would not say one word as to what air is, er- 

 as to its having any thing to do with combustion, but would 

 lead the scholar to discover that air is concerned in many 

 common changes which apparently occur spontaneously, and 

 to understand how the discovery that this is the case is made. 

 Having directed attention to the manner in which animal and 

 vegetable substances gradually decay, and are destroyed 

 when burned, and to the rusting of iron, etc., I would pro- 

 pose that such changes should be experimentally investi- 

 gated, and suggest that as -iron rusts so readily when moist, 

 the rusting of iron should be first examined : then would 

 come the question, " But how is this to be done? " Having 

 become so habituated to the use of the balance, and to ex- 

 press facts by numerical data, the student would appreciate- 

 the advice, " Let us see whether the balance will not aid us; 

 let us endeavor to ascertain whether the iron gains or loses 

 in weight during rusting." A clock-glass or saucer is there- 

 fore weighed ; some iron borings or nails are put upon it, 

 and the weight ascertained ; and, as iron is known to rust 

 more rapidly when wet, the borings or nails are wetted and 

 set aside to rust. After several days, the rusted iron is dried 

 in an oven and weighed: it is found that the weight has in- 

 creased, whence it follows that something from somewhere 

 has been added to the iron. Thus a clew has been gained, 

 and, following the example of the detective in search of a 

 criminal, this clew is at once followed up. " Wheredidthe 

 something come from? It might be the water; but is there 

 no other possible 'offender' ? Yes, the iron rusted in air." 

 This suggests the experiment of exposing wet iron in air in 

 such a way as to ascertain whether the air is concerned in 

 the rusting. Some borings are tied up in a piece of muslin, 

 and the bag is hung from one end of a piece of stout wire. 



