78 REPORT—1885. 
jections upon the plane perpendicular to the inclination-needle, of the 
movement during the disturbance of the dipping pole of such a needle 
supposed to be suspended without friction by its centre of gravity.’ 
This projection ought to be constructed by means of the declination 
variations (Ad) and those of the inclination ( A‘) ; the first being multi- 
plied by the cosine of the inclination (cos 7), in order to its reduction in 
the inclination direction. 
The readings of the three curves being made at the time of the first 
meridian, chosen at intervals of 2m., 3m., or 5m., according to the 
degree of precision which is desired, their differences are taken by com- 
parison with the first reading, and these differences should be reduced 
according to the values of the coefficients. In combining the values of 
the movements of the vertical force and of the bifilar, we find by the 
known formula (4issini cos (FZ = “* )) the variations of the incli- 
nation; these variations are projected upon the chart in vertical directions, 
having reference to the first reading, and those of the declination in 
horizontal directions, employing a convenient scale. 
Here is an example:—Four hours of the disturbance of the Ist of 
February, 1881, 0h. to 4h. (time of Pawlowsk) at Kew, and Lisbon 
readings being at the intervals of five minutes. 
Tt is noticed that all the movements are reproduced in the two figures, 
They are generally at great length, and now and then deformed at Kew 
and of different inclination by comparison with the horizontal line. 
All the movements at Lisbon and Kew are executed in the manner con- 
trary to the hands of a watch. The aspect is sooner at Kew. 
If we make a similar research upon other more distant observatories— 
for example, Pawlowsk and Toronto—the same movements are still re- 
marked ; but some aspects are completely deformed, the movements at 
Toronto being executed in the manner of the hands of a watch. 
The measurements in these researches have been taken from the 
curves of a scheme of a study of Mr. Wild upon the disturbances of 
February 1, 1881. 
VII. Observations on Magnetic Reductions. By Dr. H. Witp. 
As Messrs. Balfour Stewart and Brito Capelloin the ‘ Suggestions for 
the Committee on Magnetical Reductions,’ as well as Herr T. P. van der 
Stok in the ‘Communications of the International Polar Commission,’ 
No. 109, have clearly shown, there are to be distinguished in the varia- 
tions of the magnetic elements—Ilst, their normal daily periods; 2nd, 
the slow and constant changes which the absolute values of the days’ 
means of these show; 3rd, the eventually different daily periods which 
1 T think that it would be possible to construct a very simple instrument which 
could well register by photography all such disturbances, which would make these 
researches less laborious, avoiding all the measures and reductions which are always 
laborious. Let alittle needle be suspended conveniently by the centre of gravity, 
employing a thread of silk. In one point of this needle let there be a mirror per- 
pendicular to its magnetic axis. A luminous slit might be made to fall almost 
perpendicularly upon the mirror, registering the movement in all the directions of 
the needle. In order that these movements should not be confounded and super- 
posed, the registering cylinder should proceed by jerks from hour to hour, or oftener 
according to experience. 
