4 REPORT—1850. 
applications of this theoretical formula to the Asiatic lines of declination, I have 
discovered that the curves, which are concave to the north in the vicinity of the 
Uralian mountains, are rising northwards ; the curves convex to the north in the 
districts east of Asia are falling in a south-western direction, whilst the contiguous 
curves convex to the Chinese Sea are rising and will ultimately form one class of 
curves with those immediately north. These Asiatic curves may not be inaptly 
compared to the undulations of a wave, or to a ribbon streaming in the breeze. 
I am now engaged in the computation of a magnetic chart for the whole terrestrial 
surface for the year 1851, and shall have great pleasure in exhibiting it to the Section 
at the next Meeting. 
Notice on the Artificial Magnets made by M.Logeman, Optician at Haerlem, 
by the process of M. Elias. By Sir Davin Brewster, K.H., D.C.L., 
ΖΕ. δ. Lond. ὃ V.P.RS. Edin. 
On my return from the continent in June, I received from M. Logeman a beautiful 
horse-shoe magnet, weighing one English pound (0°482 kilogramme), which, if 
loaded with suitable precautions, such as had been pointed out by Haecker in Poggen- 
dorff’s ‘Annalen,’ vol. lvii. p.375, is capable of supporting a weight of 283 English 
pounds, or 13 kilogrammes. M.Haecker has found, from numerous experiments, that 
the power P of a magnet weighing N kilogrammes is P=10°33 J N®, but the mag- 
nets executed by the best makers in Europe have not been found to possess this 
power, or at least not greatly to surpass it. The magnet given me by M. Logeman, 
is stated to possess twice the power indicated by the formula, and with a piece of 
post paper interposed between the poles and their armature, to be still capable of 
supporting a load equal at least to that supported directly by the best magnets 
hitherto produced. 
M. Logeman mentioned that he could produce magnets of the same quality that 
would support 400 and even 600 English pounds. 
Having seen the great interest which one of M. Logeman’s small magnets excited 
when exhibited at Lord Rosse’s soirée in May, I was anxious to obtain from him, 
and dispose of for his benefit, a magnet of great power, for the purpose of exhibit- 
ing at the meeting of the Association. M. Logeman accordingly executed another 
magnet, which just arrived in time to be exhibited at one of the early meetings of the 
Mathematical and Physical Section. 
This second magnet weighed 12} English pounds, or 5.729 kilogrammes, and 
could support a weight of 150 English pounds, or 68 kilogrammes. The price of it 
was 81. sterling. 
After finishing this magnet, M. Logeman felt a desire to submit a still more 
powerful one to the Association, and after great labour he completed it in proper 
time, but owing to gross mismanagement on certain railways, it was not delivered 
to me till the meeting of the Association was over. 
This splendid magnet weighs fifty-two English pounds, or 28 kilogrammes, and 
is capable of supporting. 430 pounds English, or 196 kilogrammes. The price is 
20/. sterling. 
The permanence of the magnetism in these magnets is as remarkable as their great 
power. If the armature is torn away twenty or even a thousand times, it will still 
carry as great a weight as before. 
The process by which these magnets are made, is to make the magnet with its 
armature pass several times along a helix of copper wire traversed by a current of 
one or more elements of Grove’s battery. 
On a new Membrane investing the Crystalline Lens of the Ox. 
By Sir Davin Brewster, KH, D.C.L., F.R.S. Lond. ὃ V.P.RS. Edin. 
The Ox from whose eye the lens was taken was killed on the 13th of December, 
1838, and the lens was extracted on the 14th, at 11 a.m. 
Its thickness WAS -....seesceseeees Sebsesastitececeuatcte 0°507 
Its diameter ...... ΡΈΕΙ ὙΠ ΤΗΣ ἐξ δεν δ OWOZ 
