the lightning. This state of the compasses continued throughout the remainder of the voyage."

In 1808, a Genoese ship was wrecked near Algiers, while the captain and crew, deceived by the false indications which lightning had induced in the compasses, thought they were sailing directly away from the dangers which proved the destruction of their vessel. The effects of lightning upon the needles of sea compasses have often led to like serious consequences. Lightning may not only directly influence compass needles, but indirectly by magnetizing pieces of hard iron and steel throughout a vessel, which at once become agents in the deflection of the needles. Such deflections are sources of peril, especially as it is not an easy matter for the navigator on the high seas, even when he is aware that an error of the compass exists from such a cause, to determine its value. His condition is still more perilous when the steel pieces of his chronometers are also magnetized by lightning. Dangerous errors are, then likely to occur in the computation of geographical longitude. The chronometers of the "New York," a packet which was twice struck by lightning while at sea on the 19th of April, 1827, were found on arrival at Liverpool to be 33 minutes 58 seconds in advance of what they would have been, but for the stroke by lightning of the vessel. Adequate means should evidently be provided on every vessel for conveying away harmlessly the electric discharge.

Without considering at present, more in detail, the properties and peculiar characteristics of lightning, let us come directly to the question: Is the extent of danger from this source so great as to give importance to means of averting it? The only answer really needed to this inquiry is a reference to our daily papers during the warm season. How many accounts do we see of barns recently filled with newly made hay struck by lightning, and of them and their contents destroyed! How often we read of persons killed, buildings fired, and other injuries done by this agent. Extended statistics showing the amount of damage by lightning through a series of years are not readily obtained. Our conception of the extent of damage may, however, be aided by the following facts:

From the month of June to the 28th of August, 1797, Volney counted up in the newspapers of the United States, eighty-four serious accidents, and seventeen deaths by lightning. It is more than probable he did not obtain an account of all.

The late Charles Peirce of Philadelphia, in his statistics of the weather, kept for more than fifty years, records in 1842 sixty-one buildings burnt by lightning in the United States during the summer of that year, and forty-six deaths from the same cause. The loss in buildings which he recorded would seem to be not a large estimate of the annual loss from lightning at the present time in any one of our densely populated States.

In a statistical report made by desire of the French Government, and published in 1852, it appears that at that time, sixtynine persons were annually killed in France by lightning.

Arago, on reviewing a list of more than eighty vessels injured by lightning, found that "in fifteen months of the years 1829-30, five ships of the English Royal Navy were struck by lightning in the Mediterrenean," alone. He adds, "To those persons who say.that damage by lightning is of very little importance in a pecuniary point of view, I would add, that the mainmast of a frigate costs £200, and that of a ship of the line as much as £400.

From a reliable statement of damage by lightning in the British navy from 1799 to 1815, a period of sixteen years, it appears that 150 vessels were struck by lightning, 70 men were killed and 133 wounded, and that the loss of materials amounted to $1,000,000. In 1821, Sir W. Snow Harris, F. R. S., proposed a system of conductors which were applied to the vessels of the navy, and in 1865, or after 44 years, it was found that losses and damage by lightning had almost entirely ceased, notwithstanding the number of vessels had been greatly increased.

A magazine of gunpowder belonging to the republic of Venice, fired by lightning in 1769, occasioned a money loss of £640,000, or more than $3,000,000, and the destruction of 3,000 human lives. Explosions of powder magazines have not been so unfrequent as to lead to the conviction that means for averting such calamities should be disregarded.

Without extending to greater length these notices of deaths of individuals and losses of property by lightning, suffice it to say the number of sufferers from such accidents is sufficiently great to make it reasonable not to neglect the methods which science has suggested, and experience has demonstrated useful for avoiding their occurrence.

What are the means of protection against lightning? It is related of the ancient Thracians, that when it thundered and lightened they were wont to shoot arrows at the sky to threaten

it,—a method to which modern civilized nations would hardly deem it advisable to resort. Most precepts for personal preservation from lightning are of a negative character. Those which Franklin gave have ever been regarded as scientific and useful. For persons who, during thunderstorms are in houses not provided with lightning conductors, he recommends an avoidance of the neighborhood of fire-places. Chimneys are often struck by lightning, the internal coating of soot serving to attract it, as also the column of smoke, which rising in the air acts as a conductor for the electric fluid. Since metals attract lightning, avoid also metals, gildings and mirrors which are coated with mercury. The less the contact with the walls or the floor, the better. middle of the room is the best place unless a lamp or chandelier be hanging from the ceiling. A hammock suspended by silken cords in the middle of the room would be regarded a very safe place.

The

Among the ancients, it was generally believed that persons lying in bed were safe from lightning. This notion still obtains with many people. Facts however do not show it to be well founded. If the whole body could be enveloped in feathers, they might serve for protection; but so long as the head or any part of the body is in proximity to the bedstead, there is no immunity from the stroke of lightning, since the human body is a better conductor then are feathers or the material of a mattress.

Metals worn on the person attract lightning, and hence to an extent, are sources of danger. When lightning fell upon the prison in Swabia in 1819, of twenty prisoners together in a hall, but one was struck, and he the condemned chief of a band of robbers, was chained by the waist. Numerous examples have proved that whenever persons are struck by lightning, it particularly attacks the portions of metal worn by them. Wet clothing may be fortunate in case of lightning stroke, but with dry clothing the liability of the stroke is not so great.

Out of doors, it is a sound precept to avoid a position in proximity to tall trees. The ancients believed that certain trees are never struck by lightning. The laurel was thought to be particularly favored. The beech has been classed among trees which lightning respects. "The Chinese consider the mulberry and the peach tree as good preservatives against lightning." Observation however, shows that no species of tree can be regarded as exempt from liability to lightning stroke.

The posts supporting telegraph wires are not unfrequently struck by lightning-sometimes several posts in succession, and sometimes between the posts struck are intermediate posts uninjured. A position near telegraph posts during a thunder storm is not regarded desirable. It should not be forgotten that when lightning strikes men or animals ranged in a line, straight or curved, those at the extremities suffer most from the stroke. Bell ringers during a thunder storm occupy an unsafe place. Lightning is attracted somewhat to assemblies in consequence of the ascentional currents of warm, moist air, which serve as conductors of the electric fluid.

By what method may buildings and vessels be successfully protected from lightning? In ancient times it was thought a dwelling could be protected by surrounding it with white grape vines. Artazerxes planted swords in the ground point uppermost, to drive away clouds, hail and thunder storms. The building of large fires, the discharging of cannon, and the ringing of church bells, have been at different times among the means designed to protect towns and even extensive districts from the falling of thunderbolts.

A more rational method then any of these, is that devised by Franklin. The facts already submitted in this paper suggest the method which Franklin adopted, and point irresistably to the conclusions which he reached.

It has been shown that other circumstances being equal, lightning directs itself by preference to the most elevated portions of edifices, hence there the means of protection should be applied. It has been shown that other circumstances being equal, lightning directs itself by preference to metallic bodies. A metallic mass, therefore, placed at the most elevated part of a building, will be likely to receive the electric discharge rather than the building itself. It has been shown that when lightning falls upon a metallic mass it does damage to surrounding bodies, at the moment of quitting the metal, and in proximity to the point or points at which it escapes from it. This indicates the necessity of metallic continuity until some surface or receptacle is reached which may safely receive the electric discharge. Damp earth offers a channel by which lightning may escape from a metallic rod without producing damage of any kind. And thus we have the modern lightning conductor devised.

It is a curious and interesting fact that the Temple at Jerusalem,

which so far as can be learned from the Bible or from Josephus, remained unscathed by the lightnings of Heaven during a period of more than a thousand years. In the structure of its roof, in its covering with a coating of gold; in its long, pointed, gilt iron or steel lances, projecting from its roof; in its walls overlaid with wood thickly gilt, and in its metallic rain pipes connecting the roof with cisterns for water in the courts of the Temple, presented the most ample provision for the ready conduction of electricity; in fact, lightning rods very similar to those employed at the present day.

It is a remarkable and interesting fact, that tall pyramidal spires dating back into the middle ages-spires which have been repeatedly struck by lightning-on being furnished with lightning conductors within the last century, have had entire immunity from such strokes.

The lightning rod already devised, with reference to size, form, point and connection with the earth, should be noticed more definitely.

1st. The rod may consist of iron or copper-the former metal being generally preferred from considerations of expense, and for its greater firmness when set, by which it withstands the action of winds. It should be at least three-fourths of an inch in diameter for buildings of ordinary height. For very high structures it should be made larger. In form it is usually round, although other forms are used and serve a good purpose. A copper rod has the advantage of high conducting powers for electricity, its ratio to iron in this repect being as six to one; but it is wanting in stiffness, and is considerably more expensive than iron.*

2nd. To secure the rod from rust, it should be coated with paint containing lampblack. Galvanized iron is a good substitute for the painted rod, inasmuch as the zinc coating has a conducting capacity for electricity nearly double that of iron.

3d. Metallic continuity should be perfectly maintained throughout the entire length of the rod. So far as practicable the parts should be joined together by welding. When other joinings can

*The following table contains the electrical conductivity of several of the more commonly known metals at 32° Fah., compared with silver as a standard. The results were obtained by Matshierren by a series of careful experiments.