August 23, 1889.] 



SCIENCE. 



139 



The Barrett Mil-Ammeter. 



The mil-ammeter shown in the accompanying sketch has been 

 ■designed especially to meet the wants of the medical practitioner, 

 and, with this end in view, has been made as compact and un- 

 complicated as is consistent with accuracy. 



The question of accuracy has to be carefully considered in in- 



THE BARTLETT MIL-AMMETER. 



struments of this kind, for the present tendency in the application 

 of electricity to medicine and surgery is to obtain results based 

 upon such systems of measurement as shall be comparable at any 

 locality. 



The John A. Barrett Battery Company's mil-ammeter is be- 

 lieved to be an important improvement over most instruments of 

 Its class, and it embodies in its construction several features which 

 are entirely novel. 



Of these, the most important is the minn;r of rendering the 

 metre capable of measuring currents of very great differences in 

 value. This is secured by a system of shunts which are automati- 

 cally thrown into circuit simultaneously with a corresponding 

 change of the scale. The instrument is provided with three inde- 

 pendent scales, whose ranges are respectively 0-5, 0-25, and 

 0-250 milli-amperes. By turning a screw at the side of the case, 

 these scales are made visible one after the other, and at the same 

 time the corresponding shunt is put in action, so that correct read- 

 ings may be taken at once. 



The metre is also provided with a screw-clamp, which removes 

 the pivoted needle (the needle having a jewel pivot) from its bear- 

 ing ; and when this is adjusted, the instrument can be carried 

 around with little care and with almost perfect safety. 



Recently the range of these metres has been extended, so that 

 they now read up to 1,000 milli-amperes. 



Electrical Train Heating. 



The Burton Electric Company, of Richmond, Va., have recently 

 been making some e.tperiments with their electric heaters for rail- 

 way cars, a Sprague electric car being used for the purpose. An 

 80 volt current was used. Each heater had a resistence of 35 

 ohms, and required 2j amperes of current to raise the temperature 

 200 degrees Fahrenheit. The heater is composed of a resistance 

 coil, inclosed in a cast iron case provided with projections for in- 

 creasing the radiating surface. The wires of the resistance coil 

 are covered with powdered clay, to absorb the heat and prevent 

 the wires from being burnt out. In the experiments mentioned 

 fourteen heaters were used, absorbing three and a half electrical 

 horse-power. The heaters were connected in multiple arc. In 

 practice it is proposed to generate currents on trains under way by 

 means of dynamos driven from the car-axles, the cars to be heated 

 before starting out by currents from stationary dynamos at the 

 stations. 



eUARANTY INYESTMENT COMPANY 



CAPITAL $250,000. 



7°|o Guaranteed Farm Mortgages 7°|o 



The Company sends each year to Kansas and Nebraska for the pur- 

 pose of e.Kammlng its loans and methods of busmess a 



COMMITTEE OF INVESTORS. 



The Committee for i88q visited Fifty counties in the two States, ex- 

 amined over 100 farms on which loans had been made and reported 

 every one to be SAFE. 



The Company will be glad to send to any address the Report of the 

 Committee which presents a very interesting statement of the general 

 development of Kansas and Nebraska. 



A large number of loans equally as good as any examined by the 

 Committee are always on hand for sale. 



Address for Monthly Btilletin and Investors'' Committee Report 



HENRY A. RILEY, General Eastern iManager, 191 Broadway, N.Y. 



