382 



Dr. C. Chree. Collimator Magnets and the 



§10. Magnetic Moment. — Taking into account the variability in size 

 which we have decided to exist, it would appear from Table I that the 

 capacity for assuming permanent magnetism has been nearly the same 

 in the four groups A, C, D, and E ; but the magnets of group B have 

 been distinctly less receptive than the others. It is difficult to say 

 exactly how the magnets of group F stand. They are clearly much 

 below the average size, and their mean m is at least as large compared 

 to the means in the other groups as one would expect from a compari- 

 son of the mean moments of inertia. 



Table II shows the variability of m to have been much greater in 

 each group than that of K. 



The great variability in m is noteworthy, because when m is small, 

 corrections for torsion, temporary induction, &c, increase in relative 

 importance. 



It has been the practice of late years to reject magnets showing 

 exceptionally small magnetic moment, but the data from such rejected 

 magnets are not included in Tables I and II. 



§ 11. Temperature Coefficients. — Out of the whole 130 magnets there 

 was not a single case in which the arithmetic mean of the values found 

 experimentally for q' was negative. Thus within the experimental 

 limits, say 0° to 36° C, the rate of change of magnetic moment with 

 temperature invariably increased with the temperature. 



The mean value for q in groups C, E, and F, is practically identical, 

 and is very distinctly larger than the mean values for groups B and D. 

 Group B is specially remarkable for the smallness of the temperature 

 coefficients ; in fact, the largest value of q found in a magnet of this 

 group is very little greater than the mean value in groups A, C, E, 

 and F. 



The mean value of q' is fairly similar for the different groups, but 

 groups A and B have somewhat smaller values than the others. 



The variability of both q and q' is, as we see from Table II, very con- 

 siderable in all the groups except E, where q varies but little. The 

 term q't 2 is in general small compared to the term qt } and consequently 

 the probable error in the determination of q' is large. The variability 

 of q' may for this reason be somewhat exaggerated in Table II. 



§ 12. Induction Coefficient. — As explained above, \i is the product of 

 the volume of the magnet into its permeability, as determined by 

 reversing a field of about 0*44 C.G.S. unit, the magnet being possessed 

 of a large permanent magnetic moment. 



Table I shows that the size of the mean in the first five groups has 

 little relation to the size of the mean m. This is significant, because /* 

 and m should vary in the same way with the volume of the magnet. 



At the same time, the exceptionally small volume undoubtedly 

 possessed by the magnets of group F is almost certainly the cause of 

 the small /x found in that group ; and we shall probably be correct in 



