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THE POPULAR SCIENCE MONTHLY. 



imposed upon the teacher should be enthu- 

 siasm, life, growth. When these are absent, 

 the teacher is dead. Knowledge, to be of any 

 value to the teacher, must become a perma- 

 nent, increasing, living force in his work and 

 character. Knowledge which is non-product- 

 ive is dead. Knowledge which is alive, which 

 strengthens the memory, which guides the 

 judgment, which enlightens the reason, 

 which fortifies the will this is the knowl- 

 edge which, acting through his individuality, 

 makes the teacher a power in the school. 



Hand-marks. M. Bertillon, of the Paris 

 police, has devised a method of identifica- 

 tion by photography of parts of human bod- 

 ies. The hand being the part that is usual- 

 ly most affected by the occupation, series 

 of photographs of hands have been taken, 

 which may be compared with whole figures 

 of the same workmen at their work. They 

 show the effect upon the organ of friction 

 from tools in use. From the hands of the 

 navvy all the secondary lines disappear, and 

 a peculiar callosity is developed at the spot 

 rubbed by the spade-handle. The hands of 

 tin-plate workers are covered with little 

 crevasses produced by the acids employed. 

 The hands of lace-makers are smooth, but 

 they have blisters full of serum on the back 

 and callosities on the front part of the 

 shoulder, due to the friction of the straps of 

 the loom. The thumb and the first joints 

 of the index-finger of metal-workers show 

 large blisters, while the left hand has scars 

 made by the sharp fragments of steel. 



Tea-cnitnre. According to a Society 

 of Arts lecture by Richard Bannister, tea is 

 derived from the cultivation of two species 

 of tea plants, the Chinese and the Assamese. 

 Hybrids of various degrees between these 

 two form a great proportion of the plants 

 usually grown. In the tea-garden the plant 

 is kept down to from three to six feet in 

 height ; in a state of nature it reaches thirty 

 or forty feet, with a stem one foot in diame- 

 ter. The seed, which is inclosed in a hard, 

 round shell, ripens about one year after 

 the flower has faded. Planting is done 

 either direct from the seed itself, or from 

 nurseries where the young plants can be 

 watched carefully and tended till they are 

 strong enough to take their places in the 



plantation. Tea grows on almost all soils, 

 but one that is light, friable, and rich is 

 necessary for complete success. Close plant- 

 ing is recommended viz., four feet apart 

 equivalent to 2,722 shrubs per acre. On 

 steep slopes the Chinese variety may be 

 planted closer two feet by three and a half 

 feet, or 6,223 plants per acre. A good deal 

 of care must be devoted to pruning, with 

 the object of keeping the shrub well spread 

 and at a convenient height for picking. A 

 tea plant is picked as the successive " flush- 

 es " occur. A flush is the throwing out of 

 new shoots and leaves, the latter of which 

 form the tea of commerce. The average 

 flushing period is from seven to nine months, 

 and the intervals between flushes vary from 

 seven to fourteen days. The number of 

 flushes ranges from eighteen, where no ma- 

 nure is used, to twenty-five in good soil. 

 To a certain extent, the harder a tea plant 

 is picked, the more it becomes stimulated 

 to reproduce new shoots in the place of 

 those lost. When the season is over, the 

 tea bush is from three and a half to four 

 feet in height and about five feet in diame- 

 ter ; pruning down, its height is reduced to 

 two feet and its diameter to three feet. In 

 this state it remains during hibernation. In 

 the spring the buds at the base of the leaves 

 develop into shoots, the buds of which de- 

 velop themselves in the same way. The 

 first shoot from the branch becomes the nu- 

 cleus of subsequent flushes on that part of the 

 bush, and is therefore carefully preserved. 

 The youngest leaves give the best tea. 



Slaking Incandescent Lamps. An in- 

 candescent or glow lamp consists, according 

 to I'ajor-General Webber, from the manu- 

 facturing point of view, of the filament, the 

 wire mount, or conductor, and the glass 

 bulb. Inventors, seeking a highly refract- 

 ory substance out of which to make the fila- 

 ments, have all ended in using carbon of 

 either a fibrous or an amorphous consist- 

 ency. The form of the filament has been 

 governed by the need to hold within a bulb 

 of given size a carbon of a given length. 

 The filament must have a uniform section, and 

 that is most certainly obtained in those which 

 are formed by squirting a viscous solution 

 of cellulose into a precipitating solution. 

 The filament material is wound upon blocks 



