196 Frof. A. M. Mayer on the Magnetic Elongations 



made circuit had been broken; Dthe permanent elongations or re- 

 tractions observed in the rod after the first current passed had been 

 broken ; E the elongations or retractions produced on making 

 the second and subsequent circuits; F the elongations or retrac- 

 tions produced on breaking the second and subsequently formed 

 circuits. 



After the quantities given in the columns I have written e to 

 designate the elongation of the rod, and r to indicate its retraction. 



I have given the measures in three Tables. Table I. contains 

 the elongations and retractions in the actual scale units. It is 

 here to be remembered that one division of the scale equals 

 0*00011 of an inch for the experiments on rods Nos. 1 to 6 in- 

 clusive; while for the remaining rods, 000, 00, and 0, one divi- 

 sion of the scale equals 0*000146 of an inch. Table II. gives 

 the elongations and retractions of Table I. expressed in fractions 

 of the inch of u Troughton's scale''*. Table III. contains the 

 coefficients calculated from the numbers given in Table II. 



Certain numbers in the Tables are followed by * or by f ; 

 * indicates the maximum effect observed in the iron or in the 

 steel rods corresponding to the phase of experiment given in the 

 heading of the column in Table I., or as subsequently desig- 

 nated by A, B, C, &c. 



An examination of the Tables shows that the maxima and 

 minima effects in the case of the iron rods are very irregularly 

 distributed. Thus, corresponding to the " first make-circuit," 

 we find that rod No. 4 gives the maximum, while rod No. 1 

 the minimum. On the "first break-circuit" rod No. 2 is the 

 maximum, while rod No. 5 is the minimum. For the " per- 

 manent elongation " rod No. 4 is the maximum, and rods Nos. 1 

 and 2 are the minima. In the two columns corresponding to 

 " second make-circuit " and " second break-circuit," we see that 

 rod No. 3 gives the maximum effect observed, while rod No. 1 

 gives the minimum. 



* " Two copies of the new British standard, viz. a bronze standard. 

 No. 11, and a malleable-iron standard, No. 57, have been presented by the 

 British Government to the United States. A series of careful comparisons 

 (made in 1856 by Mr. Saxton, under the direction of Dr. Bache) of the 

 British bronze standard No. 11, with the Troughton scale of 82 inches, 

 showed that the British bronze standard yard is shorter than the American 

 yard by 0*00087 inch. So that, in very exact measures with the yard- 

 unit, it is necessary to state whether the standard is of England or of the 

 United States, as 10,000 American feet = 10,000*5803 English feet."— 

 Lecture-Notes on Physics, by A. M. Mayer, p. 12 (Van Nostrand, New 

 York, 18G8). 



