Names and Address must accompany all letters, or no attention will be paid thereto. This is for our information and for publication. References to former articles or answers should give date or paper and page or number of question. Inquiries not answered in reasonable time should be repeated; correspondents will bear in mind that some answers require not a little research, and, though we endeavor to reply to all either by letter or in this department. each must take his turn. Buyers wishing to purchase any article not advertised in our columns will be furnished with addresses of houses manufacturing or carrying the same. Special Written Information on matters of personal rather than general interest cannot be expected without remuneration. Scientific American Supplement referred to may be had at the office. Price 10 cents each. Books referred to promptly supplied on receipt of price. Minerals sent for examination should be distinctly marked or labeled. (10637)E. H. S. asks: Kindly advise me if You have a SUPPLEMENT that treats of the different kinds of molecular vibrations known to science. What I mean is this: I have been told that there are known 84 octaves of vibrations: the octave of heat above light. then light. next the photographic spectrum, and next the X-ray. Now. what I want to know is in what order do they come, and the name of each. A There may be 84 octaves of vibrations. Of that we do not know. Even if there be. not all of the octaves are occupied. The lowest number of vibrations in sound is 10 per second. The ability of the ear to hear ends at about 40,000 vibrations per second. Ileat vibrations can be distinguished for some distance below those of light. not above light, as you state. Above the vibrations of light come what are termed ultraviolet vibrations for several octaves. What may be beyond these we cannot certainly say. X-ra.vs are not vihrations in the usual sense of the term. You would he interested in this connection in Duncan's ••New Knowledge.” price $2, and in Whetham's “Recent Development of Physical Science,” price .$2. We shall be pleased to receive your order for one or both of these or any other books. (10638)W. J. H. asks: 1. When the ship crosses the line of the equator, does the needle in the mariner's compass deflect arid point to the south pole? A. A magnetic needle has two ends: one end is directed to- wa rd the north. and the other toward the south pole of the ea rth. A II over the world civilized people use the north end of the compass needle to steer by : the Chinese use the south end. There i, no change whatever in the magnetism of a needle upon crossing the equator, nor in its use as a guide to a ship or traveler. It is wholly a matter of usage by which end one shall steer. 2. Is there any rlifference in the “istance that a cannon will send a ball on either the land or the sea? A. Water and land alike have no effect upon the distance a cannon ('an throw a shot. The pressure of the gas in the gun alone determines the distance the ball will go. (10639)A. H. G. asks: 1. In the case of electrolysis of water system by overhead trolley ca r system. is the eating away of pipes where the current enters or leaves the pipe? A. The electrolysis of water pipes and other metal hy the return current of the trolley lines takes place where the current leaves the pipes or metals. 2. In modern pra('tice, is it suffi- ficient to have electric welded joints or rails. or should a return wire hp provided : if SO. should it he overhead or underground ? A. If the rails are properly welded, no better provision for the return of the current under ground can he made. No wire is required. (10640)J. V. G. H. writes: When gathering some wild flowers this morning T found (among an ahundance of our common rod or lilac thistle) a thistle with pure white hlossoms. Will you kindly inform me if tias is a common occurrence? Also about the possible explanation for this loss of color, and whether they continue white in coming years, and even would originate a new species? A. The common thistle occasionally has white flowers. We do not know whether this peculiarity could he transmitted hy the seeds or not. One would hardly care to propagate thistles even to determine so interesting a question. It is quite common in many plants that white flowers appear in place of those of the usual color. It is also true of animals. This is not conside red as the origination of a new species. This variation in the thistle is mentioned in the botanies. (10641)H. W. .T. writes: 1. To what degree of heat has wire glass been tested without yielding in any way? 2. To what degree has it been heated and then played upon by a flre hose without yielding? I have had some very high figures given anil would like correct information. A. The claims on behalf of wire glass, as we understand them, are not so much that it does not “yield” ( in the sense of cracking) under hi!(h temperature whether followed by a stream of cold water or not. hut that it remains in place after being cracked. preventing sudden drafts accelerating a fire. We have no conclusive figures covering the tests you descrihe, hut are endeavoring to obtain them and hope to give them later. WATERBURY COMPANY LIFE IN THE NAVY Would you like a good position paying $16 to $70 a month and “free living expenses, with a chance to increase your earnings by various allowances-a position that will give you a liberal pension if disabled—a position in which thirty years' service entitles you to retirement on three-quarters pay? There is an opportunity in the Navy for the young man of good character, sound health and ambition ; there is a chance for the man with a knack for mechanics to fit himself for a trade at the naval schools—to prepare himself to earn a good living either in or out of the Navy—an opportunity to develop a sound physical body, to breathe pure fresh sea air, to indulge in various forms of athletics. Anyone who proves himself especially capable may become a warrant officer, and later try for a commission. SnfiClHl advantages are offered to men with a trade. If you OpeViai auramagvo are a mechanic, an electrician, a stenographer, an accountant, a drug clerk, or a baker or cook, you can enlist at an increased rate of pay at the start, and serve at your trade, taking advantage of the different trade schools—there being no cost for tools or text books, and your pay and living continuing just the same. If you would like to know all about life in the Navy, send for an illustrated booklet, It tells you about the opportunities offered, ' all about a department of the government service that is fascinating and attractive for the young man of ability and high aspirations who wants to serve his country while he helps himself—a service in which the opportunities for travel exceed those of any other government position. It also describes fairly the hardships to be endured in the Naval Service. Address BUREAU OF NAVIGATION. Box Navy Department Washington. D. C.