JuLy 10, 1902] 
every three and a half years are the true cause of the 
pressure changes ; and that the varying intensity of solar 
activity within the sunspot period of eleven years pro- 
duces an effect on the pressure and circulation of our 
atmosphere, thus affecting the whole globe meteoro- 
logically. 
(8) The close correspondence between the epochs of 
these subsidiary pressure variations and those represent- 
ing prominence frequency suggests, not only their very 
close relationship, but that the terrestrial pressure quickly 
answers to the solar changes, while so far as the work 
has gone it would appear that rainfall ( Fig. 2, Curves 
A, B, C, D) and snowfall are subsequent effects. 
(9) It may be remarked that we have already obtained 
evidence showing that this short-period variation is not 
the only one acting, but that the eleven-year and thirty- 
five-year periods apparently influence the short-period 
variations. But even this does not explain some 
anomalies already met with, and should the solar origin 
of these short-period pressure changes be subsequently 
confirmed, some of them not constant in all localities 
will have to be explained: and it is possible we may 
obtain in this way some new knowledge on the atmo- 
spheric circulation. 
(10) The period of time included in this survey begins 
generally with the establishment of the full records of | 
the Indian Meteorological Department in 1875 and 
extends to 1895, when the regularity of the widened- 
line phenomena was broken, as stated in a previous 
| things and how to deal with them, and to be induced to 
| leave the learning sought at leisure from books alone 
| and that is supported only by unrealities of arguments 
communication. 
Addendum, dated June 26. 
In continuing the above researches we have plotted the 
percentage frequency of the solar prominences derived 
from the Italian observations for each 10° of solar lati- 
tude N. and S. of the equator. 
We find that the epochs of maximum prominence dis- 
turbance in the higher latitudes are widely different from 
those near the equator. The latter are closely associated 
with the epochs of maximum spotted area, the former 
occur both N. and S. at intervening times. 
We have, then, two sets of strongly marked promi- 
nence outbursts occurring at intervals of between three 
and four years. 
Both sets are represented closely in the Indian pressure 
curves. 
Solar Physics Observatory. 
LHE FIRST MAGNETICIAN. 
ge (es booke is not for every rude and unconnynge 
man to see, but for clerkys and very gentylmen 
that understand gentylness and scyence.” 
This quotation from Caxton is prefixed by Prof. 
Thompson to his notes to the new edition of the “ De 
Magnete.” 
Most students of electricity know that William Gilbert 
of Colchester is the father of the sciences of magnetism 
and electricity. They may have some idea of the extent 
of his discoveries and the general character of his work, 
NATURE 
but few who have not seen the celebrated book in which | 
he recorded his results can have really grasped how much 
Gilbert knew and how thorough and complete were his 
investigations. 
“He practised the experimental method of obser- 
| of the theory of electricity. , 
| writes, ‘‘a conspicuous force of attraction manifests itself 
249 
science are due to him and to all who have helped him 
for enabling them to learn what Gilbert did. 
It was a happy thought to found the Gilbert Club, and 
the members of the club who have the chance of possess- 
ing this splendid volume, the outcome of many years of 
| patient research and loving labour, are greatly to be 
envied. 
The club was founded in 1889 to commemorate 
Gilbert’s work and to issue a translation in English ; at 
that date there was none, though one was published in 
America in 1893 The original edition was issued in 
1600, and it was at first hoped that the translation might 
be ready in time for the tercentenary celebration at 
Colchester in 1900. This proved impossible, but the 
work is now complete and the result is admirable. 
It will be of interest here to give a brief account of 
the work itself. Starting with the early history of the 
loadstone, its power of attracting iron known to the 
ancients and its property of setting in a definite direction 
discovered in the tenth or twelfth century, Gilbert in 
the first book of his treatise sets forth the various funda- 
mental properties of a magnet and of magnetised iron, 
illustrating them by the experiments now familiar to all, 
and describing almost in every chapter some new dis- 
covery or some important law. He is continually 
appealing to experiment and accurate observation. 
““Deplorable is man’s ignorance in natural science,” he 
writes, “and modern philosophers like those who dream 
in darkness need to be aroused and taught the uses of 
and by conjectures” But Gilbert lived too early ; it was 
more than 200 years before the truth of his maxim was 
realised. 
He was quick to appreciate at their true value the in- 
accurate observations of some who had gone before him. 
“Albertus Magnus writes,” we are told, “that a load- 
stone had been found in his day which with one part 
drew to itself iron and repelled it with the other end ; 
but Albertus observed the facts badly ; for every load- 
stone attracts with one end iron that has been touched 
by a loadstone and drives it away with the other.” 
Among other things, we may note his observation that 
“a long piece of iron (even though not excited by a 
magnet) settles itself toward north and south”; but 
perhaps the greatest discovery in this book is contained 
in the last chapter, ‘That the globe of the earth is 
magnetick and a magnet,” our “ New and unheard of 
doctrine about the earth” he calls it. The doctrine is 
proved by the observations and experiments which are 
the subject of the rest of the treatise. 
Book ii. deals with a number of examples of magnetic 
attraction, and in chapter ii., ‘‘On the magnetic coition, 
and first on the attraction of amber, or more truly on 
the attaching of bodies to amber,” we find the beginnings 
“For in other bodies,” he 
otherwise than in loadstone ; like as in amber, concerning 
which some things must first be said that it may appear 
what is that attaching of bodies and how it is different 
from and foreign to the magnetical actions, those mortals. 
| being still ignorant who think that inclination to be an 
vation before Bacon wrote about it ; his methods and | 
discoveries excited the sneers of Bacon, the praises of 
Galileo and Kepler.” : 
The book justifies the high claim put forward on its 
behalf by its latest editor, and the thanks of men of 
attraction and compare it with the magnetic coitions,” 
and so to illustrate electric actions he invents the straw 
electroscope. He divides bodies into “ electricks,” which 
are electrified by friction and attract light bodies, and 
“non-electricks,” the metals and other conductors as 
| we now call them. The effect of heat and moisture is 
i “* William Gilbert of Colchester, Physician of London, onthe Magnet, | 
Magnetic Bodies also, and on the Great Magnet the Earth.” Pp. 246. 
Published in Latin, 1600. Translated and edited for the Gilbert Club, 1900, 
with notes by Prof. S. P. Thompson, F.R.S. a 
NO. 1706, VOL. 66] 
studied and described, and the distinction between 
electrical and magnetic attraction fully made out. 
With amber or other ‘‘electricks,” “if indeed either a 
sheet of paper or a piece of linen be interposed there 
will be no movement. But a loadstone without friction 
