A CONVENIENT LAMP BANK.

BY P. C. HYDE,

Newark Academy, Newark, N. J.

The lamp bank, of which a diagram is here shown, was devised to combine as many utilities as possible in a single piece of apparatus that should be at once simple and safe. It is used as a demonstration and laboratory piece, and as a lamp rheostat.

As appears from the diagram, there are eight lamps and eight switches, all of the latter single pole, three double throw and five single. The board is wired in front, and built large enough so that the lamps do not hide the wiring when the apparatus is hung against the wall of the lecture room. The position of the switches, open ones showing white on a white background, makes it easy for pupils to trace the path of the current at each

stage of a demonstration or experiment. For added distinctness the copper switch blades are painted black to correspond with the wiring.

The binding posts are connected to a three-wire current supply, direct or alternating. For lamps in parallel A is down (towards the binding post), H likewise, B is up, and the other switches are closed. Single lamps are extinguished by opening in succession H, G, F, E, D, C, and B. With A, B, and H all down and the other switches all closed, the lamps are connected on the threewire system; the effect of blowing a neutral fuse, and the necessity of the neutral wire to keep the voltage even when the sides are unbalanced, is shown by opening A, which puts the lamps in multiple on 220 volts. By connecting an ammeter, preferably zero centered or alternating current, in the neutral line, the value of the current in the middle wire for unbalanced three-wire operation is clearly shown. With an ammeter in each line, the neutral current is shown to be the difference of the other two, a fact essential to the economy of the system.

With H up and the other switches open the lamps are in series, and individual lamps are cut out by closing in succession A, B, (both up), C, D, E, F, and G. The increasing current can be shown clearly by the changing glow of a 15-watt tungsten lamp adjacent to H if the other lamps are 16 c.p. carbons, as the total resistance of the latter is not sufficient to dim entirely the small lamp.

A careful examination of the diagram will show that no possible combination of switches will short-circuit either line. The only combination to be avoided is A up and B down, as this throws 220 volts across a single lamp or row of lamps. With C open and an old lamp adjacent to B it is not a bad plan to try this combination before a class, to show the need of care in testing out live wires with an incandescent lamp where there are voltages above 125, and the danger of operating unbalanced circuits in multiple.

The bank is neither difficult nor expensive to construct. The switches are of the ordinary 125 volt 15 ampere baby knife type, and the binding posts should have composition caps for protection against shock. The wiring is 14 double braid. The apparatus has proved itself decidedly convenient and instructive, and fool-proof when operated by students on a 110-volt line. Its versatility can be fully appreciated only after considerable

use.

THE RELATION OF RÖMER AND FAHRENHEIT TO THE THERMOMETER.

TRANSLATED BY WILLARD J. FISHER,

Worcester, Mass.

(Ole, or Olaf, or Olaus, Römer was born at Aarhus, Denmark, September 25, 1644; died at Copenhagen, September 19, 1710. In 1662, he became pupil and amanuensis of E. Bartholin, in Copenhagen, who employed him in classifying the manuscripts of Tycho Brahe. In 1671, he helped J. Picard redetermine the geographical position of Tycho's observatory, Uraniborg. In 1671 or 1672, he went with Picard to Paris; there he be came mathematical tutor of the Dauphin and member of the Academy of Sciences, and was occupied with observations in the royal observatory and the king's hydraulic works at Versailles and Marly. In 1674, probably before Desargues and La Hire, he invented the epicycloid and indicated its applications to gear teeth. September 22, 1675, he read his paper on the velocity of light as deduced from observations of the eclipses of Jupiter's first satellite. About the same time he was interested in the design and construction of planetaria. In 1681, he returned to Copenhagen, as royal mathematician and professor of astronomy in the university. He also became mayor, chief of police and privy councilor. On his advice, Denmark adopted the Gregorian calendar.

He invented the transit and prime vertical instruments and the meridian circle, and used altazimuth circles and the equatorial mounting for telescopes. His realization of the importance of clock rate in meridian work led to an interest in expansion and contraction and a fundamental improvement in thermometers, as shown below. His observations and papers perished in the Copenhagen fire of 1728, with the exception of three night's work, preserved by Horrebow, 1735, and discussed by Galle, 1845, the Adversaria, mentioned below, and, of course, a few published in the proceedings of the Berlin and Paris academies. At the time of his death he was engaged in attempts to discover stellar parallax, which would inevitably have led him to the discovery of aberration, for reduction of his work has shown it to be of almost modern precision.

Accessible works are, R. Grant, Hist. of Phys. Astr., p. 461; Doberck, Nature, 17, p. 105, 1877-78; See, Pop. Astron., No. 105, May, 1903. A portrait of Römer is to be found in LaCour and Appel, Vol. I.

I find slight discrepancies among the various reference works as to dates and facts of Römer's life; Doberck's article is very full.

Kirstine Meyer, née Bjerrum, has written in Danish a book on The Development of the Temperature Concept in the Course of the Ages, published, 1913, in the series, Die Wissenschaft. Her account of Römer's part in the development of the thermometer is here translated from this German edition. It appeared first in Archiv für die Geschichte der Naturwissenschaften und der Technik, 2, p. 323-349, 1910.-W. J. F.)

From occasional expressions in the scientific literature of the eighteenth century, on which I came accidentally, I inferred that probably Ole Römer had busied himself with the construction of thermometers, and that there had been a relation between him and Fahrenheit. I will later come back to these expressions. They led me to search in the libraries and archives at Copenhagen for works by Römer, and only at last in the University Library; for I had to assume that the papers of Römer in possession of this library had been destroyed by the conflagration of 1728. Yet there I found what I sought, namely, Römer's Adversaria, in manuscript, in a volume of miscellanies.1

A note on the last page tells how the book came into the possession of the library, and that it escaped the fire through being then in the possession of Römer's widow, remarried to Th. Bartholin. She gave it to the library in 1739. This note says: "Da mein erster Gatte Olaus Römer Sel. diese cahiers in Pergament hat heften lassen, möchte ich annehmen, dass er sie selbst als von einiger Importance erachtete, weshalb ich dieses Volumen in der Bibliotheca Academica geborgen wissen möchteunter anderen Manuscripten, damit jemand darin, wie zu vermuten, etwas Nützliches darin finden könnte. E. M. Bartholin, Witwe von Th. Bartholin Sel., in octobre 1739."

This book contains a whole section on the thermometer and, besides, a few isolated remarks on temperature measurement. Römer's form of the thermometer seems to me to be of great interest; he is apparently the first to construct the thermometer with two fixed points, namely, the temperatures of melting snow (nix sine gelu et calore) and the boiling point of water, and with a division of the tube into equal volumes.2 This happened in 1702, partly according to Römer's own notes, partly according to Horrebow's. In Adversaria, p. 131 b., there is a reference to Amonton's comparison between his own and Newton's statements of equal temperatures; Römer makes a brief extract from the comparison tables, and adds:

"The observation of the incipient freezing and of the boiling of water seems to me in the highest degree adapted for application in the construction and graduation of a universal thermometer, as the former point is sufficiently well fixed, and the latter, contrary to my earlier view, deserves confidence; for, according to the concurrent observations and reliable assurances of the French, boiling water, once the boiling has begun, cannot increase its temperature."

In 1703, then, Römer seems to have been clear about the principle. Horrebow has made marginal notes at various places in the Adversaria, from which it appears that Römer made his thermometers about 1702. He writes,5

This Adversaria, written mostly in Latin, has been published by the Royal Danish Scientific Society on the occasion of the two-hundredth anniversary of Romer's death, under the editorship of cand. mag. Thyra Eibe and Dr. phil. Kirstine Meyer.

2On this see translator's note at end.

3Mem. de l'Academie Roy. des Sciences, 1703, p. 100.

"Roy. Soc. Phil. Trans., 22, p. 824, 1700-1701. On this scale the ice point is zero, body heat 12, water boiling violently 34; this makes body heat 35.3 C.; cf. 36.9, actual mean. I do not know that Newton ever attempted to construct a thermometer giving these readings, and I think the original shows that he did not consider the boiling point of water a constant, in spite of the observations of Halley and others.-W. J. F.

Adversaria, p. 118 b.

"1741, on April 10, I asked Römer's widow when he had made the five thermometers. She answered, they had been made in her presence; she could not, however, recollect any contemporaneous event, through which the date could be determined; but at that time Römer could not get out, owing to a broken leg. Consequently it was before 1703, the year in which, in June, I came to Römer's observatory, for Rumohr, John and other assistants were telling that he had been dangerously ill with wound fever after a broken leg.

"On 17 April, Römer's widow came to me and said, now she knew certainly that these thermometers had been made in 1702."

The section of the Adversaria which deals with thermometers, etc., consists of eleven folio pages. The first heading runs, "On the calibration of glass tubes for thermometers." A solution is given of the problem, so to divide thermometers with various sized bulbs and bores, that the divisions shall agree; i. e., so that the volume of ten divisions shall everywhere have the same ratio to the volume of the bulb. He finds the diameter of the tube by means of a quicksilver drop; this he puts into the tube and measures its length, then he weighs it and calculates its volume, assuming that a cubic foot of quicksilver weighs 837 pounds. From this we see that he takes the specific gravity of quicksilver 13.5, as in the system of measures used by him a cubic foot of water weighs 62 pounds.

After he has determined the length and volume of the drop, he calculates its diameter, and so the diameter of the tube, at the region where the drop lies. That Römer is interested in this connection with the problem probably depends on this: that on several sides, as, e. g., by R. Hooke, it had been proposed to make mutually agreeing thermometers on the following principle: one fixed point, and a division of the tube into equal volumes, which should in all thermometers be in the same ratio to the bulb volume.

After solving this problem he gives a suitable formula, and adds that this really has nothing to do with his investigations, which were for determining the irregularities of the tube bores, usually conical or of irregular form.

"I investigate their form by means of a quicksilver drop before the bulb is blown on. In the tube previously mentioned I have found a sufficiently regular part, so that at the middle a "It had previously been mentioned that Horrebow had used these.