May I, 1891.J 



SCIENCE. 



25P 



class. Another greit advant ige in instruments of this type is the 

 fact that they are not affected by proximity to masses of iron or 

 dynamo-machines. 



Several styles of tangen galvanometers are also included in this 

 list. Fig. 6 illustrates them. This instrument, properly adjusted, 

 can be used as a standard instrument for laboratory work with 

 entire satisfaction. The brass ring is thirteen inches and a half 

 in diameter, and the groove in which the wire is wound is care- 

 fully turned so as to be of perfectly rectangular cross-section, thus 

 allowing the constant of the instrument to be carefully calculated, 

 and compared with the constant as obtained by other methods. 

 The whole instrument has been specially designed to meet the re- 

 quirements of teachers in laboratory practice who desire to make 

 students entirely familiar with all the adjustments of the standard 

 galvanometer before putting a high-grade instrument in their 

 bands. The compass-box, five inches in diameter, is so held m 

 position that it may be raised or lowered, rotated on its vertical 

 axis, shifted out of the plane of the coil, etc., thus enabling the 



student to acquire proficiency with the instrument, and to meet 

 all cases of derangement possible. 



The dial is graduated to single degrees, while a mirror under it 

 allows readings to be made without error of parallax. The needle 

 is suspended by a very light cocoon fibre. The whole instrument 

 can be turned about its vertical axis, and a quadrant graduated 

 to degrees upon the base allows the amount of rotation to be 

 accurately measured, and the laws of the sine galvanometer in- 

 vestigated. 



Of resistance-boxes, this list offers a variety. Fig. 7 is a com- 

 bination Wheatstone bridge and resistance-box having twelve coils, 

 and, in addition, bridge-coils of 10, 100, and 1,000 ohms on a side, 

 thus giving a total range of measurement of from .01 of an ohm 

 to 111,000 ohms. Separate keys, properly connected, for battery 

 and galvanometer, are mounted on the same top with the set. 



Queen's '-New Model" reading telescope (Fig. 8) will please- 

 many who have long been seeking something of the kind, reliable, 

 and at the same time reasonable in price. 



In dyspepsia the stomach 

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