[l':ntered at the Po.t Office Of New York, N. Y., as Second Cia •• Matter. Copyright. 18m. by ;\hnln It Co.] ------------------------------ A WEEKl.Y JOURNAl. PRACTICAl. INFORMATION, ART, SCIENCE, MECHANICS, CHEMISTRY, AND MANUFACTURES. OF Vol. ��!�::;'l�: 11' A. YEAR. E J NEW YORK, SEPTEMBER 11, 1897. [$3.00WEEKLY. HOW TO BUILD A SMALL ALTERNATIWG CURRENT cal power required to drive it, an alternating current, considered entirely apart from the armature in a sep­ DYNAMO WITHOUT CASTIWGS. known as a"single phase." Alternators are built for arately excited machine, whether the armature is of BY NEVIL lIrONROE HOPKINS. lighting and power transmission, both .. single phase" the tooth type or ring type. The only relation which N umel'OUS small books have been published on and .• polyphase," although the .. polyphase" gener­ we need consider in the machine which we are build­ dynamo building, but they have been mainly devoted ators are principally employed for power transmission. ing is in the number of field magnets. If we use ten to descriptions of direct current generators. The little In the alternating current dynamo the voltage rises field magnets and consequently ten poles, we must machine described in the following article produces a and falls in a very rapid periodic manner, driving a make the armature with ten teeth, if of the tooth type; "single phase" alternating current at 110 volts pressure, wave of electricity first in one direction, then in the or, should we make a ring armature, the ring must be and is built without patterns and castings. The making reverse, with great rapidity. The field magnets can be wound with ten coils equidistant. The armature given of small dynamos is is the tooth type, but frequently given up is conveniently re­ by amateurs because moved, leaving the patterns and castings shaft and hub to re­ are required. Pat­ ceive a ring arma­ terns are often trou­ ture, with the col· blesome and expen­ lector rings ready to sive to m a k e, and be connected to the iron castings are not new and different.ly always procurable in designed armature. the average town. The term "period" The iron ring which used in connection forms the frame or with an alternator body of the alter­ denotes the time nator described in elapsing between one this connection can complete reversal of be quickly made by the cur r e n t. The almost any black­ .. frequency" is the smith, and is to be number of double re­ preferred to a casting versals of the current if made from good per second. The fre­ soft iron. For a larger quency varies in dynamo than the one practice between 150 described the i ron and 25. It will be ring can be very readily seen that 1(he easily made by using greater the number blacksmith's rollers, of pole san d the known as tire bend­ greater the speed at ers. The little ma­ which the machine chine, when its field is driven, the greater magnets are only will bethe frequency. feebly excited, gen- Fig. 1. Fig. 2. Alternators are in­ erates the most ap- variably d esign e d proved kind of alternating current for with more pole pieces than direct cur­ medical purposes, as the voltage is rent machines, in order to get the re­ steaQY; consequently furnishing a cur­ quired number of re\'ersals of the rent which is free from the jerking or current every second. If the frequency twitching sensation so common with is not high enough, lamps, for instance, the use of induction coils. With the in circuit, would flicker. If only two fields strongly magnetized the machine, or four poles were employed in our when run at about 2,000 revolutions alternator, the armature would have per minute, is capable of lighting a 50 to revolve at a dangerously high speed candle power 110 volt lamp. As the to obtain the required frequency. The designing of alternate current dyna­ number of pole pieces for alternators mos, mathematically considered, is vary from six to one hundred and over. rather beyond the average amateur, The largest slow speed machines which the author merely gives the result of are designed for direct connection to calculations, except in the matter of the driving engine have over one hun­ field magnet winding, where a choice dred poles.. Alternators for commer­ of wire presents itself, in order that the cial use are usually designed to give a field magnets made shall be suitable voltage between 1,000 and 3,000. This for any exciting current at the com­ high voltage is desirable for power mand of the user. The mathematical transmission at great distan c e s, designing of alternator a I'ma t u res whether for lighting or motor work. would take up more space than our By the use of transformers immersed limits allow. The armature as described in oil for high insulation, the voltage is readily detachable from the shaft and is conveniently"stepped up" to 30,000 collector rings, leaving an excellent and power transmitted one hundred field for experimentation with different miles, and" stepped down" by trans­ types of armature cores and windings. formers to any voltage desired. The The electrical engineer whose knowl­ transformations of current and voltage eo,ge becomes deficient when he leaves without altering the actual value, or direct current dynamo machinery and electrical horse power, are very beau­ deals with generators of alternating tiful. For example, if we have at hand type has a very limited field for prac­ 25 amperes at 2,000 volts tension, or tice, as the alternating current machine pressure, we lllay exchange the 2,000 has come to the front to remain, dis­ volts for more amperes and vice versa placing the direct current generator in without altering the power to do work, many important branches of electrical which is the definition of energy. An engineering. There are to-day many armature could, of course, be wound electrical men who are at home, so to to produce a current at 20,000 volts, speak, when dealing with the applica­ but the all-important electrical term tions of current electricity, and are .. insulation" would forbid it. Assum­ badly at sea when they meet with ing the machine were wound for 20,000 problems pertaining to alternating cur­ volts, the amperage would only be 2'5; rents. The alternator we are about to Again, should an accident happen to build is the simplest form at present the transtoi'mer insulation, when under in actul\l use, being excited by a bat­ the tension of 20,000 volts, the primary tery, or other source of direct current, and secondary windings might come and delivering, in place of the mechani- A HO][E-][ADE ALTERNATING CURRENT DYNA][O. (Continued on page 165.) © 1897 SCIENTIFIC AMERICAN, INC. I SEPTEMBER I I, I �7. THE ANTIQUITY OF 1I4N IN AMERIOA. know how Turner mastered the electric flash, which is Sir John Evans, the new president of the British As­ the most bewildering and most evanescent of all things, 'citntifit �mttican.p sociation, has attackad our paleolithic pretensions. For and where scientific investigators who apparently had ESTABLISHED 1845 years it has been thought that the State of New Jersey a stronger motive for ascertaining the exact truth, fail, was at one time inhabited by men who were the con­ he succeeded, though he might be 8upposed to have been MUNN & CO., EDITORS AND PROPRIETORS. temporaries of the post-glacial men of Europe. Sir moved chiefly by his plastic sense with no reference PUBLISHED WEEKLY AT John Evans, the highest living authority on the an­ to scientific accuracy. tiquity of man, tells us the chipped stone implements No. 361 B�OADW A Y. NEW YORK. found in the Trenton gravels are not paleolithic at all, THE BRITISH ASSOOIATION MEETING.-II. but were probably made by the red Indians. Such In addition to the mention in last week's issue of TERMS FOR THE RcmNTIFIC AilIERICAN. words coming from so eminent an anthropologist will the SCIENTIFIC AMERICAN of papers presented at the (Established. 1S4;,).) probably cause a re-examination of the entire subject recent meeting of the British Association at Toronto, . S3.UO One copy, one year, for the U, S., Canada or Mexico . ................ we subjoin a brief synopsis of what was said by some One copy, six months, for the U. S., Can.ida or Mexico ... ..... ..... 1.;')0 of the Trenton implements now that the ax of scientific One copy. one year.to any foreign country,Dostage prepaid, £() 16s. 5<1. 4.00 doubt has assailed the family line ascendant of the other eminent scientists at the meeting. Prof. A. W. Remit by postal or express money order. or by bank draft or check. original inhabitants of America. Walker, lecturer in St. Mary's Hospital, London, pre­ MUNN & CO., 361 Broadway, corner Franklin Street, New York. Chipped flint weapl;ms, which showed no signs of sented some curious records, obtained photographi­ The �"Ientiflc American Supplement (Established 181'6) grinding and polishing, totally unlike those found at cally, showing the 18 a distinct paper from the SCIENTIFIC AMERICAN. THE 8UPPI,EMEN'l' the surface, have been discovered at the bottom of EFFECT OF VARIOUS DRUGS ON THE NERVES. is issued weekly. Every number contains 16 octavo pages, uniform in size e r f P thick beds of gravel in the valley of the Sornrne, at 11� �c;::r����ct}}:¥r���gan�� :�� �e����� 1���a ��a��;r l�lE����d�: He had two sets of electric wires connected with the to foreign countries belong ng to tho;;,Postal UnI n.