28 Questions for Solution relating to Meteorology, 



Inclinations, — In general it will be attended with little ad- 

 vantage to bestovv much care on observing the diurnal variation 

 of the horizontal magnetic needle, in places where the expedi- 

 tion is not stationary for a whole week. It is different, how- 

 ever, with the other magnetic elements. Wherever the Bonite 

 stops, though it be only for a few hours, it is desirable to mea- 

 sure, if it can be accomplished, the declination, the inclination, 

 and the intensity. 



While attempting to reconcile the observations on the incHna- 

 tion, made at remote periods in different regions of the earth, 

 not far distant from the magnetic equator, it has been ascertain- 

 ed, some years since, that this equator is advancing progressively 

 and entirely from the east to the west. At present it is sup- 

 equator. Thus, in the southern hemisphere^ the point of a horizontal magnetic 

 needle which turns towards the south, will move from east to west from 8| o'clock 

 in the morning till 1|: in the afternoon, and from west to east from 1^ p. m. till 

 the morning of next day. This observation, at least, accords with reason. But 

 let us compare the simultaneous movements of two needles, when referring 

 them to the same point, that namely which is turned towards the north. In 

 the southern hemisphere, the point turned towards the south moves from east to 

 west from 8i o'clock in the morning to \\v. m., at the same time the nortli 

 point of the same needle makes the contrary movement. Thus to put it de- 

 finitively, in the southern hemisphere, the point turned towards the north moves 

 from west to east from 84 o'clock a. m. till 1| p. m., which is precisely the op- 

 posite of the movement made by the same north point, at the same hours, in 

 our hemisphere. 



Let us suppose that an observer, starting from Paris, advances towards the 

 equator. As long as he continues in our hemisphere, the north point of his 

 needle will make a movement every morning towafUs the west; in the other he- 

 misphere, the 7iorth point of the same needle will move every morning towards 

 the east. It is impossible that this change from a western movement to an eastern 

 movement can take place in a sudden manner. There must necessarily be, be- 

 tween the zone where the first of these movements was observed and that 

 ■where the second takes place, a line where, in the morning, the needle will 

 neither move to the east nor to the west, that is to say will remain stationary. 



Such a line must exist ; but where is it to be found ? Is it the magnetic 

 equator, the terrestrial equator, or some curve of equal intensity ? 



Researches, continued during many months, in the places situated between 

 the terrestrial and magnetic equator, such as Fernambouc, Pay ta. Conception, 

 the Pelew Islands, &c., would certainly lead to the desired solution. But 

 many months of assiduous observation would be requisite ; for, notwithstand- 

 ing the skill of the observer, some brief intermissions in the investigations of 

 Captain Duperrey, undertaken at Conception and Payta, at the request of the 

 Academy, have still left some doubts on the subject. 



