TRANSACTIONS OF THE SECTIONS. 13 
3 a.m., which is followed by a maximum about 5 a.M., or a little after. These fluc- 
tuations are small. A second and principal minimum takes place at 10" 10™ a.m. ; 
and a second or principal maximum about G p.m. The mean daily range is ‘0024 of 
the whole intensity. 
In the summer months the smaller maximum and minimum disappear, the inten- 
sity decreasing continually throughout the night, but slowly, until 5 or 6 a.m., after 
‘which the decrease becomes rapid. ‘There are, consequently, but one maximum 
and one minimum in the mean daily curve, which correspond nearly in epoch with 
the principal maximum and minimum of the curve for the entire year. In the winter 
months, on the other hand, there are three maxima and three minima, the even- 
ing maximum appearing to break into two. The epoch of the morning maximum 
moves forward as the time approaches the winter solstice, appearing to depend upon 
the hour of sunrise, which it precedes by a short interval. The epoch of the principal 
minimum is nearly constant throughout the year. The daily range is greatest in the 
month of July, when it is about -0045 of the whole intensity ; it is least in the month 
of January, being then about -0008 of the whole. 
Total Intensity and Inclination.—The total intensity appears to vary very little 
throughout the day. It seems to be least about 9 a.m., and then to increase, attaining 
a double maximum in the afternoon. The total range however being very sinall, the 
variations of the two components of the intensity are dependent chiefly upon the 
changes of the inclination. 
The inclination is greatest between 10" and 10" 30™ a.m., and least about 6 p.m., the 
epochs corresponding with those of the least and greatest values of the horizontal in- 
tensity. The daily range is about 2 minutes in the early part of the year, and in- 
creases to more than double of that amount in summer. 
If we combine the changes of declination and inclination, the former being multi- 
plied by the cosine of the absolute inclination, we obtain the whole movement of the 
north end of the magnet in free space, or the curve formed by the intersection of the 
magnetic axis with the sphere whose radius equals unity. The whole movement 
during the first six hours of the day is inconsiderable. 
It appears, on a review of these facts, that the diurnal changes in the direction of 
the magnetic force are (as might be expected) connected with the diurnal movement 
of the sun, and its times of rising and setting. The changes of the intensity appear to 
od aa in addition by some other cause, or by the same cause operating less 
rectly. 
Professor Lloyd concluded his paper by an account of the annual changes in the 
pean of the magnetic force at Dublin, as far as they have been hitherto deter- 
mined. 
On the Circumstances which affect the Energy of Artificial Magnets. 
By the Rev. W. Scorgssy, D.D., F.R.S. 
The object of this communication, Dr. Scoresby stated, was not to enter into the 
extensive bearings of the subject announced, which the time of the Section would not 
allow; but he might just state, in general terms, that the energy of permanent arti- 
ficial magnets, of which alone he designed to speak, was affected by a considerable 
variety of circumstances, all acting by laws peculiar to themselves, and thus occasion- 
ing differences in the resultant energy whenever any of the circumstances might be 
changed. These circumstances comprised quality of steel, denomination (such as cast 
steel, shear steel, blister steel, &c.), temper or hardness, mass, and form. Hence, from 
the varying influence of these several circumstances, it was impossible to give a gene- 
ral answer to the inquiry, as to the best kind and temper of steel for permanent mag- 
nets. In large magnets, indeed, consisting of considerable combinations of bars or 
heavy masses, he, Dr. Scoresby, had sufficiently determined the fact, that best cast 
steel, made as hard as possible, was the most effective; but for small magnets or thin 
compass needles, shear steel, or cast steel tempered, became most effective. In a six- 
inch bar which he exhibited, of 600 to 700 grains’ weight, hard cast steel was advan- 
tageously employed ; but in thin plates, used singly or in pairs, such hardness required 
to be reduced. But by extensive investigation of the effects of these several condi- 
