292 CURRENT TOPICS. [J. F. I.

those in which several different industries are concerned and which are approved by the central national body. These include funda- mental engineering standards as : Standard diameters, tapers, sizes of keys, threads, fits, etc. ; materials; tools; measuring instruments and gages; machine parts, including handles, ball and journal bearings, etc. ; gears and sizes of paper.

A striking example is cited of the efficiency of national standard- ization as it has been developed in Germany, in the case of a rush order placed with German manufacturers for two hundred locomo- tives for delivery to Russia. Production of different parts was allotted to seventeen different manufacturers to be produced strictly upon the plan of interchangeable parts, no one manufacturer making a complete locomotive. No serious practical difficulty was encountered in filling the order. The inspectors made a particularly striking test of the feasibility and accuracy of the plan by ordering a complete loco- motive to be assembled from parts chosen at i-andom from the parts furnished by the seventeen manufacturers. It proved to be ready for service immediately after assembly without the necessity of any dis- assembling for readjustment. H . L .

A Magnetic Shield Made of Iron Tape. CARL BENEDICKS. (.,~nn. d. Phys. 72, No. 3. )--The problem of protecting a galvanometer against magnetic disturbances was at first satisfactorily solved by the use of a massive protecting shield. This failed to protect the instrument ade- quately when the disturbing force became greater. It thereupon be/:ame necessary to discover a better method of protection. It has been known for some time that a nest of iron shields, one surrounding another, gives good protection. In fact such a nest reduces the influ- ence of an external magnetic force upon the central cavity more than is done by the same mass of iron in one solid piece. Following. a suggestion of Lebedew, Esmarch built an effective shield of iron w~re with the layers separated by cardboard. The author tried the effect of shields made by winding soft iron tape on a form with interposed layers of paper. He found that such a shield weighing 2.75 kg. reduced the deflection caused in a galvanometer by an external mag- netic force to one-eighth of that still remaining when a solid heavier shield weighing 4.2 kg. was in use. The lighter shield reduced the deflection to about ~ per cent. of its amount with no shield. The thickness of the paper made little difference and the use of a copper band likewise seemed to be without influence. G . F . S .

¢ PRESS OF

j . E. L I P F I N C O T T C O M P A N Y P H I L A D E L P H I A