April 19, 1889.] 



SCIENCE. 



293 



AYRTON AND PERRY'S IMPROVED AND NEW 



AMMETERS AND VOLTMETERS. 



We take pleasure in placing before our readers a description of 

 the latest instruments of the well-known electricians, Professors 

 Ayrton and Perry. Quite a full description of these remarkable 



production of instruments without permanent magnets, they having 

 found out by experience, that, no matter how well such magnets 

 are aged, they will change in their strength, which makes them 

 unfit for instruments which will be very accurate for any length of 

 time. They discovered some years ago that a spring made of fiat 

 ribbon wound in corkscrew fashion will produce a very great rotary 



FIG. I. — HOT-WIRE VOLTMETER. 



instruments has just appeared in the London electrical journals, 

 and has been copied in the American journals. We are, however, 

 in a position to give some very important data recently received di- 

 rectly from Professors Ayrton and Perry, through their sole agents 

 in the United States, Messrs. James W. Queen & Co., Philadelphia. 

 This additional information not only covers great improvements 



motion on one end free to move, while the other end is held in its 

 place. This spring is used in all their new instruments, the per- 

 manent magnets having been discarded as early as 1883. Ayrton 

 and Perry have perfected the methods of testing and calibrating their 

 instruments, and we shall soon be able to give a full illustrated de- 

 scription of their laboratories. 



FIG. 2. —HORIZONTAL SECTION OF HOT-WIRE VOLTMETER, 



which they have made in their well-known magnifying spring in- 

 struments, but also a full description of the hot-wire voltmeter, the 

 first samples of which have just been received by J. W. Queen & 

 Co. It is a well-known fact that the practical instruments which 

 Ayrton and Perry have invented are now more largely used than 

 any instrument upon the market. If we examine the work of these 

 two eminent men in the line of testing-instruments, we will see that 

 they have been largely devoting themselves of recent years to the 



Very extensive experiments and investigations have furnished the 

 necessary data to make these spring instruments the most accurate 

 technical instruments in the market. It is very interesting indeed 

 to follow Professor Ayrton's general reasoning, which gives a mathe- 

 matical law to even the most minute things in reference to these 

 instruments. Among his latest discoveries is that platmoid wire is 

 the best material to wind voltmeters to reduce the errors of tem- 

 perature influence. In a very interesting description of the testing- 



