54 REPORT—1845. 
almost as much precision, as such determinations can be made with the most 
recent instruments, and in a manner which will probably leave little to be de- 
sired on that head. 
We shall also have determined satisfactorily the mean values of the diur- 
nal variations ; including under that expression, the effects both of the so- 
called irregular disturbances, now ascertained* to have a sensible mean influ- 
ence on the diurnal variation of the magnetic direction and force, and of the 
more regular diurnal fluctuation connected with the sun’s hour angle. In 
the first two years of the Toronto Observations these effects have been 
in a great degree separated from each other, and the mean values of each 
ascertained. ' 
In respect to secular changes, we have learnt that neither the instrumen- 
tal means which were originally furnished, nor the methods of observation 
originally directed, were fully competent for this part of the inquiry; and 
we have substituted a system of absolute determinations made monthly with 
instruments subsequently contrived, combined with the observations of the 
differential instruments used with various precautions stated in the pub- 
lished volume of the Toronto Observationst. This process has already 
been some months in operation, and we are able to say with confidence that 
it will accomplish the purpose, if a sufficient time be given. I fully con- 
cur with those who consider,,that the endeavours which we are making, to 
place on record and transmit to posterity the present magnetic state of the 
globe, would be deficient in a most essential particular, if they failed to deter- 
mine the secular changes which are at present taking place at our stations of 
-observation. 
There is also a very important class of determinations which are in progress 
of accomplishment by the same improved means that have been resorted to 
for the secular changes, which yet require some further time for their satis- 
factory completion. I allude to the annual variations of the magnetic ele- 
ments. The evidence brought forward in the volume of the Toronto Observa- 
tions appears to leave little doubt of the general fact, that the terrestrial 
magnetic force is at that station considerably greater in summer than in 
winter, and that the annual variation forms a regular progression intimately 
connected with the march of the temperature{. The complete establishment 
of this important fact in terrestrial physics, and a satisfactory measure of its 
mean value at each of the stations, together with similar determinations in 
respect to the annual variation of the magnetic direction (which is also indi- 
cated at Toronto, though in a less decided manner), may be confidently 
expected by perseverance in the means which have been adopted in the last 
few months. 
For the sake therefore of the secular and annual changes, I concur in opi- 
nion with those who desire a somewhat longer continuance of the magnetic 
observations at the stations which are now occupied ; though I am at the same 
time of opinion that an observatory starting with our present instruments, and 
our present methods of observation, might be expected to satisfy in a reason- 
able manner ail the desiderata which have been mentioned, in a period of five 
ears. 
i With respect to the sémultaneous observations made at the periods now fa- 
miliarly known by the nate of magnetic term-days, the objects sought were 
of a less definite character, and it is therefore not so easy to say to what ex- 
tent the purposes which called them forth have been fulfilled by what has 
already been done. Much has undoubtedly been learned respecting the phae- 
* Toronto Observations, pp. xxvii and xlix. 
T Pp. xi. xxxiii. 1. vii. (note). t Pp. xxxvii. ef seq. 
