April 29, 1892,] 



SCIENCE. 



249 



ballast bear some particular and constant ratio to the motion 

 of this short-period pendulum to keep the balance true. The 

 inertia of a heavy mass will cause some loss of time, as we 

 can only use a limited force for its control; but it is possible 

 to accelerate the phase of motion and overcome this difficulty 

 so far as to get good results. 



"If, now, we imagine the ship to roll in still water, the 

 effect of the combination just described will be to balance 

 the ship's stability for a limited angle; but this defect is re- 

 moved by the introduction of a second pendulum of long 

 period, which tends to move the ballast in the opposite 

 direction to the first one, and enables the apparatus to dis- 

 criminate between the angular motion of the water and that 

 of the vessel. 



" I find, however, that the long-period pendulum is rather 

 a delicate instrument, and that its function can be served by 

 a cataract arranged so as to always slowly return the ballast 

 to the centre, and this device has the effect of accelerating 

 the phase of motion, which, in some cases, we also re- 

 quire. 



" We are therefore able, by very simple parts, to construct 

 an appai'atus which will indicate the direction and amount 

 of motion necessary to be given to the ballast at a particu- 

 lar time so as to resist the wave effort; this power of indi- 

 cating may be converted into one of controlling by suitable 

 mechanism. The loss of time due to inertia of the necessary 

 ballast is not always unfavorable when the apparatus has to 

 extinguish rolling motion, the greatest effect being obtained 

 when the ballast crosses the centre line of the ship at a time 

 when it is most inclined to the water surface, and this cor- 

 responds to a quarter of the phase behind the motion of the 

 short pendulum." 



The apparatus has been working for some time in the 

 steam yacht " Cecile " with very good results. What the 

 objections may be to applying it to the largest passenger 

 steamers remains to be seen. A moving weight of some- 

 thing like 100 or 150 tons would probably be required in such 

 vessels. The power necessary to control the movement of 

 the weight appears to be small, and Mr. Thornycroft's in- 

 vention seems at any rate to show the way towards obtain- 

 ing the long-desired boon of substantially reducing, if not 

 checking altogether, the rolling of ships. If it succeed in 

 doing upon a large scale only a portion of what is claimed 

 for it in the way of anticipating and counteracting the heel- 

 ing effect of waves, without the possibility of acting in an 

 erratic or undesirable way, we may hope to see it adopted 

 some day in passenger steamers. 



LETTERS TO THE EDITOR. 



»** Correspondents are 7'equested to be as brief as possible. The writer^s name 

 is in all cases required as proof of good faith . 



On request in advance, one hundred copies of the number containing his 

 communication will be furnished free to any correspondent. 



The editor will be glad to publish any queries consonant with the character 

 of the Journal. 



A Fire-Bali. 



A TELEPHONE wire was supported on cedar posts 20 feet high 

 and 30 rods apart. During last August [1889] we had a thunder- 

 storm, during which there was a sharp and heavy crash. Several , 

 of the poles were found to have been struck, and portions to have 

 been taken out through their entire length. One of these por- 

 tions, of the size of a medium rail, was thrown into an adjoining 

 field some rods from the pole. Portions from the others were 

 smaller and more or less shattered. Near the southernmost pole 



struck, a family were in a house with doors and windows open, 

 and a luminous ball seemed to leap from the wire, pass through 

 the open door and a window, and pursue its course some rods 

 through the open space behind the house. A boy in the room 

 grasped his thumb and cried out, " I'm struck," and Mr. Hewett 

 felt a sensation of numbness in his left arm for some time. A girl 

 seized her shawl and rushed out of the house to chase the ball. 

 She reported that she pursued it some distance, while it bounded 

 lightly along, until it seemed to be dissipated in the air without 

 an explosion. The size of the ball was about that of the two fists, 

 and its velocity about that of a ball thrown by the hand. 



C. C. Bayley. 



Lightning. 



The account of a stroke of lightning in Science for Jan. 29 last 

 and the article in the issue of April 8 on "The New Method of 

 Protecting Buildings from Lightning " call attention to a subject 

 which has been greatly neglected, viz., the nature, characteristics, 

 and effects of lightning strokes. Besides the passage of the elec- 

 tricity from the cloud to the earth, or the reverse, heavy dis- 

 charges are always accompanied by other phenomena, which vary 

 on different occasions, and which, for want of record and tabula- 

 tion, have not yet been explained and their laws determined. In 

 the loose accounts given of them in our daily journals they are 

 spoken of as " freaks of lightning," and no further notice is taken 

 of them. In the hope of doing something towards making a 

 careful record, I offer the following, which has never been pub- 

 lished. 



The village of Amherst, Mass., is supplied with water from a 

 reservoir among the Pelham hills, about five miles distant. The 

 aqueduct runs nearly in a straight line from east to west. The 

 pipes are made of thick sheet-iron bent into tubes, and the over- 

 lapping edges are riveted together with copper rivets about two. 

 inches apart. They are covered both without and within with a 

 thick coat of cement. The joints are filled with cement so that 

 the irons do not come in contact, an iron ring five or six inches- 

 broad is slipped over the joint, and the whole covered with cement. 

 At a place about half a mile west of the reservoir the aqueduct 

 runs near the foot of a steep hill that is seventy or eighty feet 

 high and covered with a recent growth of white pine, shrub oaks,, 

 and yellow birch from ten to thirty feet in height, the intervals of 

 the trees being filled with bushes. During a very heavy shower 

 in July, 1884, a thunder-bolt was seen to fall on the hill. It struck 

 a pine tree half-way down the side of the hill, whose top, on a 

 horizontal line, was not more than two rods from the bottom of 

 the trees on the summit. The tree struck was about twenty-five 

 feet high and eight inches in diameter at the butt. The lightning 

 did not apparently strike it on the top, but about one-fourth of its 

 height from the top, at three equidistant points on the circumfer-- 

 ence the bark began to be ruptured, and the ruptures continued in. 

 straight lines to the ground. There the three currents united, ran, 

 over the ground, scattering the dirt and leaves in all directions for 

 two rods, until it came over the aqueduct. There it bored a hole an 

 inch in diameter down to the pipes. It struck about the middle 

 of one of the lengths, broke the cement, and indented the iron as 

 with a heavy blow of a sledge-hammer. The surface of the in-, 

 dentation appeared to have been melted. The current then 

 turned to the west, ran along the top of the pipes, which were full 

 of water under heavy pressure, stripped off the cement and slit 

 the iron tubes through the whole, or a part, of their length. When 

 a line of rivets came in its path, it cut them off between the 

 overlapping edges of the iron as smoothly as with a knife, leaving 

 the parts in each edge undisturbed. At the joints it rent off rings 

 and cement, and indented the edge facing the current, melting 

 the surface as in the place where it first struck the pipe. Rarely 

 was the edge from which the current flowed indented. These 

 effects continued for more than a mile, growing less and less, and 

 finally disappeared. 



Several questions in this connection require solution. 



1. If the discharge is simply the equalizing of the potential be- 

 tween the cloud and the earth, why was that not accomplished ag. 



