POPULAR MISCELLANY. 



281 



from an eminent teacher. This method, 

 were it applied to the whole working litera- 

 ture of education, would place the judgments 

 of the best teachers at the service of all the 

 people. Of the catalogue of this library the 

 Bureau of Education is printing twenty 

 thousand copies. 



Thickness of Oil Films. From experi- 

 ments made in the Baltic Sea off Greifswald, 

 Prof. Oberbeck, of the University of Greifs- 

 wald, has found that the surface of water 

 calmed by one litre of rape-seed oil or ma- 

 chine oil oscillates around nineteen thousand 

 square metres, indicating that the thickness 

 of the film is about one twenty-thousandth of 

 a millimetre. The oil doubtless extends also 

 in an imperceptible film outside of the circle 

 of calm, whence the average thickness of this 

 inner layer is probably even less. The author 

 has made skillfully devised series of labora- 

 tory experiments to determine still more pre- 

 cisely the minimum thickness of a percepti- 

 ble film, and found it to be two millionths of 

 a millimetre. This is the same thickness as 

 that which Lord Rayleigh found adequate 

 to arrest the movements of camphor. Mr. 

 Rontgen has also found that the vapor of 

 ether striking upon oil scatters it till it is re- 

 duced to the same thinness. According to 

 Herr Oberbeck, a film six times thinner is still 

 coherent. If the quantity of oil is gradually 

 increased the pellicle becomes more and more 

 resistant, and of uniform thickness. When 

 it reaches eighteen millionths of a millimetre, 

 the oil collects in droplets which lise above 

 the rest of the surface ; and the film does 

 not become uniform till enough oil has been 

 poured on to equal the entire thickness of 

 the droplets. 



Advances in the Dairy Indnstry. At 



the Dairy Building at the World's Fair there 

 were daily demonstrations of the best mod- 

 ern practice in butter and cheese making. 

 Prof. S. M. Babcock, of the University of 

 Wisconsin, the chemist in charge, as part of 

 his apparatus, employed the milk tester in- 

 vented by him in 1890. This tester is used 

 by adding to milk an equal quantity of sul- 

 phuric acid of 1"82 or 1'83 specific gravity. 

 The mixture is poured into a series of glass 

 bottles, each drawn out at the neck as a 

 narrow and calibrated tube ; the bottles, laid 



in an inclined position on a frame, are rotated 

 YOO to 1,200 times per minute ; the sulphu- 

 ric acid separates the fat, and this fat, by 

 centrifugal motion, is sent up into the cali- 

 brated tubes, where it is easily read off. 

 This test places the dairy industry upon a 

 business footing, and not only enables the 

 propi'ietor of a butter or cheese factory justly 

 to appraise the milk he buys, but also de 

 cides for the dairyman which of his cows is 

 most profitable and which should be sent to 

 the butcher. The importance of tliis simple 

 and ready test is evident when we learn that 

 in Wisconsin alone there are 1,700 butter 

 and cheese factories. The Babcock tester 

 is manufactured by some twenty firms in the 

 United States, and by a firm in England and 

 a firm in Germany. Due as it was to the 

 experiments of a servant of a State, the de- 

 vice has not been patented. To this fact is 

 in part due the wide sale of the tester ; it is 

 so simply manufactured that no costly pat- 

 terns and plant are needed for its produc- 

 tion ; at retail the price is but eight to 

 twelve dollars, according to size. To his 

 forerunners in the task of fat testing Prof. 

 Babcock declares his indebtedness. Mr. 

 Short, of the University of Wisconsin, had 

 invented an apparatus in which milk fat was 

 saponified and driven forth by centrifugal 

 motion ; Prof. Patrick, of Iowa, employed, 

 in a tester of his design, an acid instead of 

 an alkaline combination. Uniting an idea 

 from each of these devices, Prof. Babcock 

 hit upon success. 



Vegetarian Pedestrians. The result of a 

 pedestrian contest recently completed be- 

 tween Berlin and Vienna was a triumph for 

 two vegetarian walkers, who came out a long 

 way ahead of their carnivorous competitors. 

 The fact corresponds with other evidence of 

 the enduring power of non-meat-eaters. If 

 there is one thing certain, says an English 

 journal, remarking on the achievement, about 

 the races that eat no meat, it is that they 

 can march. " Thousands, probably scores of 

 thousands of Sikhs and Hindostanees would 

 have performed the German feat, and not 

 have thought at the end of it that they had 

 done anything wonderful ; and they not only 

 eat no meat, but they are the descendants of 

 men who have eaten no meat for perhaps 

 two thousand years. They have eaten wheat 



