50 REPORT——1845. 
disturbances (pp. xxi. and xlix.), the variations of the vertical force (p. Ixii.), 
and of the inclination (p. Ixv.), require a longer series of observations. We 
may hope that the years 1843-45 will have done much to clear away the 
doubts remaining on these particular points, but they certainly cannot afford 
such a complete elucidation of the variations comprehended within longer 
periods, otherwise called secular variations, as may be capable of forming a 
perfectly solid foundation for all future researches. To allude only to one 
instance; the secular change of the inclination at Toronto during the last 
three years has been found to be so small, that it cannot even be discovered 
in which direction it takes place. As we cannot assume that there is no such 
change, or that it is always so small as to escape detection even by such exact 
observations during an interval of three years, we must suppose that at To- 
ronto the inclination was stationary at that time. But such a moment is, for 
all future investigations concerning the nature of the magnetic forces, of an 
importance similar for instance to that of the perihelion of a planet for the 
determination of its path, and to break off the observations before this and so 
many other no less important points are properly established, would be greatly 
lamented by those men of science who may devote their activity to this 
branch of science either in the present or in the ensuing century. 
If however there are many points which from their very nature cannot be 
settled by a six years’ series of observations, there are others certainly for 
which the evidence will be complete ; or if anything be still wanting, it will 
be owing solely to the incompleteness of the instrumental means which have 
not yet attained to that high degree of perfection to which we are accustomed 
in the apparatus belonging to other kinds of observation. The diurnal varia- 
tion and all the quantities depending thereon are of this class; and even for 
the variations comprised by longer periods, the monthly and annual variations 
for example, most of the circumstances belonging to them will be known, if 
not with certainty, yet with a high degree of probability. 
If, then, as is assuredly wished and hoped by all who take part in investi- 
gations of this nature, the magnetical and meteorological observatories esta- 
blished by the British government be continued for some years longer, the 
secular variations and the laws of disturbances should be regarded as the 
principal objects to be kept in view, and the activity of the different establish- 
ments should be directed accordingly. In this view it might suffice if four- 
hourly observations were substituted for hourly or two-hourly, taking for in- 
stance, 0, 44, 84, 12, 16" and 20%, and employing not Gottingen time but the 
time of the station, as the special object in view is to obtain a thorough know- 
ledge of the phenomena as they present themselves at the place of obser- 
vation, inasmuch as their march depends in almost all cases on the position of 
the sun relatively to their own meridian, not to that of another and distant 
station, a principle always followed in meteorological observations. In mag- 
netic terms, no doubt strict simultaneity of reading is always desirable, but 
the daily observations at fixed hours should I think be taken by the time of 
the station, as has hitherto been done in meteorological terms, The magnetic 
observations, if made at fixed hours each day, might be taken doubly by re- 
peating the reading of each element at the end of five minutes. By this 
means, the presence of disturbance, which might escape detection by a single 
observation, would often be discovered, and with well-established instruments 
properly protected against currents of air, the alterations taking place in those 
short intervals would also furnish inferences concerning the diurnal march, 
The magnetic term days, which were principally designed for the more 
accurate investigation of the laws of disturbances, have not perfectly answered 
to this view, because few of the greater disturbances occurred on the pre- 
Kon 
