32 REPORT—1846. 
Santis gives by twenty-four manipulations a strong spark and shock felt in the 
elbows. 
On some Results of the Magnetic Observations made at General Sir T. M. 
Brisbane's Observatory, Makerstoun. By J. A. Broun. 
1st. Magnetic Declination.—The annual diminution of westerly declination at 
Makerstoun is 5'"8, When proportional parts of this have been added to the monthly 
means, from January 1844 till August 1846, their whole range is only 2"1; that is 
to say, the mean position of the magnetic needle for any month, freed from secular 
change, has not been above 2'1 further west than the mean position for any other 
month. Mr. Broun conceives that he has found the annual period of westerly decli- 
nation to consist of a minimum at the vernal, and of a maximum at the autumnal 
equinox; the mean range being under 1/2. From the observations for 1843, Mr. 
Broun has concluded that there is a maximum of westerly declination when the sun 
and moon are in opposition, and a minimum when they are in conjunction ; that there 
is a maximum of westerly declination when the moon has its greatest north, and also 
when it has its greatest south declination, minima occurring when it crosses the 
equator, In the diwrnal period, the double maximum and minimum have been found 
to exist in eachJmonth of the year. In the Transactions of the Royal Society of 
Edinburgh, Mr. Broun has given certain results relating to the horizontal and vertical 
components of the earth’s magnetic force; but these results were obtained in scale 
divisions corrected for temperature by his method. In order to deduce the variations 
of magnetic dip and of the total magnetic force from the variations of these compo- 
nents, it was necessary to determine the values of the scale divisions in known units. 
Mr. Broun had previously shown* the inapplicability of the method given by the 
Committee of Physics of the Royal Society of London for the balance magnetometer. 
He now described a method by which the value of the micrometer divisions may be 
satisfactorily determined. This method will be found in the Introduction to the 
Makerstoun Observations for 1843. He has applied the same method to the bifilar 
magnetometer, and has found that the value of the scale divisions, obtained in the way 
recommended by the Committee of Physics, is also inaccurate for this instrument. 
With the aid of the values obtained by the new method, the following results have 
been deduced. 
2nd. Magnetic Dip.—tThe dip is a minimum when the sun and moon are in con- 
junction, and a maximum when they are in opposition. In the mean diurnal period 
for the year, 
The principal maximum occurs at 10° 10™ a.m. 
Me minimum is 5 40 pm. 
A secondary maximum ,, Bit AOU Asis 
o minimum —,, 5 40 a.m. 
Makerstoun mean time being always used. These periods vary to some extent 
throughout the year, the principal minimum occurring at 6 a.m. in winter; the two 
minima being nearly equal at the equinoxes, and the diurnal curve being single in 
summer. Mr. Broun has found that there is a maximum of dip about four hours and 
a half before the moon’s passage of the superior meridian ; a minimum about half an 
hour after that passage; a secondary minimum about three hours after it; and a se- 
condary maximum about eight hours after it. 
8rd. Total force of the Earth’s Magnetism.—A minimum occurs when the sun and 
moon are in opposition, equal maxima near the quadratures, and a secondary mini- 
mum at the time of conjunction. In the mean diurnal period for the year, 
The principal maximum occurs at 55 40™ p.m. 
oa minimum se, 2 10 a.m. 
A secondary maximum _,, 7 10 a.m. 
> minimum ,, 10 10 a.m, 
The periods of maxima and minima shift about two hours in the course of the year, 
and in summer the principal minimum occurs at 10" 30" a.m, The variations of 
force with reference to the moon’s hour angle were found by Mr. Broun as follows :— 
* Transactions of the Royal Society of Edinburgh, vol. xvi. 
