of Electro-Magnetism. 
tween the two fluids, and which tends to place the poles of 
either £tt right angles to those of the other and to the right 
line which joins them. By admitting this species of action, the 
formula above given is immediately deduced, and all the experi- 
mental deviations at every azimuth, and at any distance, and 
with any length of conducting wire, as readily computed ; and 
the coincidences, as above stated, are in every case to the high- 
est degree satisfactory. The same theory is equally applicable 
to the explanation of the very interesting rotatory experiments 
of Mr Faraday, and, in short, to every phenomenon that has yet 
been observed in this new branch of natural philosophy. 
Art. XVI. — Observutimis on the Natural Family of Plants 
oalled Polemoniacea ; with Descriptions (f the Genera he~ 
longing to it^ and of a Genus improperly rferred to that 
Order hy Botanists. By Mr David Doxf, Curator of the 
Lambertian Herbarium. 
ISJoTHiNG, certainly, has contributed so much to the rapid pro- 
gress of systematic -botany in our days, as the journeys of scien- 
tific travellers in distant countries, and the formation of exten- 
sive herbariums. The Order PolemoniacetR^ established long 
ago by Professor de Jussieu, in his admirable Genera Planta- 
rumy has, however, received little addition or illustration since, 
either by himself or others. But as the advancement of every 
science must necessarily be slow and progressive, and, as every 
addition leads to fresh discoveries, so in botany, every new dis- 
covery serves powerfully to illustrate the relative affinities of 
orders, genera, and even species. The ample advantages I have 
enjoyed during the period my al tendon has been directed to 
this subject, in having the extensive collections of Buiz and 
Pavon under my immediate inspection, besides other plants 
belonging to this order, from the Abbe Cavanilles, have enabled 
me to render the present essay on the Poleinoniacem much more 
complete than I could otherwise have made it. The results 
will, I trust, prove not unacceptable to botanists. 
The Order Polemoniaceae is characterised by a regular mo- 
nopetalous, pentandrous, 5-lobed corolla, by a triple stigma ; a 
