CONTENTS.

PART II.

INVESTIGATIONS CONCERNING THE LAWS OR PRINCIPLES
AFFECTING THE POWER OF MAGNETIC STEEL PLATES
OR BARS IN COMBINATION.

CHAPTER I.

AS

TO THE POWERS OF COMBINATIONS OF MAGNETIZED
PLATES OF TEMPERED STEEL IN CONTACT

RESULTS

CHAPTER II.

ON THE POWERS OF

PAGE

97 - 109

COMBINATIONS OF MAGNETIZED

STEEL PLATES, SEPARATED BY LIMITED SPACES - 119

Sect. I. Of the relative Powers of Combinations of Magnetized
Steel Plates, as affected by changes in the TEMPER of the SAME
SERIES of Plates
Sect. II.

·

Of the Magnetical Powers, separately, and in combination, of Steel Plates variously tempered, both in extent of surface, and in degree of hardness

Sect. III. Of the Magnetic Powers of Combinations of very hard
Plates and Bars

1. As to hard Plates

2. As to hard Bars in combination

RESULTS

PAGE

133

153

159

- 159

- 168

- 175

CHAPTER IV.

ON THE RELATIVE POWERS, IN COMBINATION AND SEPA-
RATELY, OF HARD PLATES OR BARS OF STEEL OF
DIFFERENT DENOMINATIONS AND QUALITIES

ON

- 185

Sect. I. Of the Magnetical Powers, in combination, of Steel
Plates (7.5 inches in length) of different denominations, but
of the same original quality of Iron`

1 Experiments with Steel of different denominations,
converted out of Stubs's Steel

2. Experiments with Steel of different denominations,
converted out of best Swedish iron, marked hoop-L
Sect. II. Of the Magnetical Powers, in combination and
separately, of Steel Plates (7.5 inches in length) of similar
denomination, but of different qualities of the original iron

THE

CHAPTER V.

- 189

. 189

195

196

MAGNETICAL POWERS OF STEEL PLATES OF
DIFFERENT MASSES, DENOMINATIONS, AND QUALITIES,
AND MEASURES OF COMBINATION, PREPARED FOR
THE NEEDLES OF SEA-COMPASSES, WITH THE EFFECT
OF SPACING THE PLATES.
- 202

Sect. I.-Experiments with Plates for Compass-needles of best
cast-steel, tempered equally throughout, at a spring temper 204
Sect. II.-Experiments with Plates for Compass-needles, of
superior qualities of steel of various kinds and denominations,
made quite hard

1. Experiments with five series of 6-inch Compass-plates, being 0.56 inch broad

2. Experiments with five series of 7.5 inch Compassneedles, of 0.75 inch in breadth

ON

CHAPTER VI.

OF HARD

THE EFFECTS OF THE ANNEALING
STEEL PLATES OF DIFFERENT KIN D AND MASSES,

ON THEIR MAGNETICAL PROPERTIES, BOTH SINGLY
AND IN PAIRS

Sect. I. On the Effects of annealing Hard Steel Plates in
boiling linseed Oil

PAGE

214

- 223

- 223

. 226

228

Sect. II. On the Effects of annealing on hard Steel Plates, in
hot Oil, at various degrees of temperature
Sect. III.--On the Effects of annealing, at various Temperatures,
on the Magnetic Powers of hard Steel Bars, single and com-
pound, of the Horse-shoe form
RESULTS

ON THE

§ I. Results in respect to difference of Denomination in the
same quality of hard Steel

§ II. Results in respect to difference of Quality in the same
denomination of hard Steel

§ III. Results as to the Changes in Magnetic Properties
produced in hard Steel of different denominations and
qualities by annealing in boiling linseed Oil

§ IV. Effects of annealing on the Energy of hard straight-
bar or plate Magnets, at degrees of temperature inferior
to that of boiling Oil

258

. 260

§ V. Results on the Magnetical Capacities and Powers of
Steel Plates, or Bars, adapted for Sea-compasses, both
single and compound, whether hard, or whether
annealed at various temperatures, with the Effects of
spacing the Plates

§ VI. Results in respect to the peculiar Effects of hardness
and annealing on Magnets of the Horse-shoe form

CHAPTER VII.

POWERS OF HARD STEEL BARS COMBINED IN
VARIOUS WAYS, AS ALSO IN PROPORTIONAL MASSES,
SO AS TO FORM COMPOUND MAGNETS OF LARGE
DIMENSIONS AND OF GREATER LENGTHS THAN THOSE
OF THE ORIGINAL ELEMENTARY BARS; WITH A
PRELIMINARY
CONCERNING THE
METHODS OF DETERMINING THE RELATIVE POWERS
OF MAGNETS OF DIFFERENT LENGTHS.

INVESTIGATION

266

270

Case I.-Comparison of the Powers of various Bar-magnets
of the same length (viz. six inches), as determined by the
methods of Torsion and of Deviations, in order to the further
verification of the method of Deviations

289

Case II.-The Determination, experimentally, in Magnets of
different lengths, of the relation of their respective deviating
effects (at distances from the Compass proportional to their
several lengths) to their actual directive powers

Case III. The comparative Capacities for Magnetism of equi-
valent, or similarly proportioned, Bars of Steel of different
lengths, as Determined both by the method of Deviations and
that of Torsion

Sect. I.-As to the proportional Powers of Magnets of different
lengths, but in all other respects, both as to dimensions in
breadth and thickness, and in quality and hardness of Steel,
the same

Sect. II.-As to the proportional Powers of Magnets combined
as in the figures (plate iv.), compared with those in a single
pile, or fasciculus

PAGE

- 292

295

310

313

- 315

Sect. III. As to the relation of the Powers of Bars of twelve
and of those of eighteen inches when combined so as to con-
stitute masses of the same form, dimensions, and weight
Sect. IV. As to the relative Powers of Combinations of twelve
or eighteen inch bars, each kind by itself, and those of equal
masses and dimensions composed of the two kinds, intermixed 316
Sect. V.-As to the relative Powers of various Combinations of
Bars of the same description (except as to the length of the
integrant bars) in proportional masses

· 317 Sect. VI.-As to the extent to which small Magnets, made quite hard, may be advantageously combined, with a view to the formation of larger artificial Magnets than have yet been constructed

GENERAL RESULTS

- 319

CHAPTER VIII.

OF THE MAGNETICAL POWERS, RECEPTIVE AND PERMA-
NENT, OF CAST IRON, BOTH IN SEPARATE BARS
OR PLATES, AND IN VARIOUS COMBINATIONS OF
PLATES

RESULTS

- 330

- 344

CHAPTER IX.

ON THE MEASURE OF

IN

PERMANENCY OF THE ENERGY
STRAIGHT-BAR MAGNETS, BOTH SINGLE AND
COMPOUND, AND OF DIFFERENT DEGREES of HARD-
NESS, AS SELF-SUSTAINED, OR AS INFLUENCED ONLY
BY TERRESTRIAL MAGNETISM

RESULTS

348

- 361

AS TO THE POWERS OF COMBINATIONS OF MAGNETISED PLATES OF TEMPERED STEEL, IN CONTACT.

THIS important object of inquiry-as affecting both the directive power of compass needles and the energy of compound magnets--has been pursued to a much greater extent, and with a much larger variety and assortment of plates and bars, than it may here be necessary, or indeed useful, to describe.

In the whole, the powers in combination of about forty sets of plates or bars, have been carefully tried, in their respective series of from 2 to 192 together, -the total amount of magnetised pieces of steel, subjected to experiment, being scarcely less than from seven to eight hundred. And in several of the sets of bars or plates, the powers in combination were likewise

H