372 



NATURE 



\_Feb. 17, 1 88 1 



observer of the heavens. In the Bibliof>raphie Astronomiqi(e 

 we find an astronomical work printed in 1625, attributed to liiui 

 as Willem Jansz Blauvv. 



It will be seen from the works of Kepler and Cassini that 

 Blaeu's star (34 Cygni of our present catalogues) at no time rose 

 higher than the third magnitnde, though even Madler {Populare 

 Astronomic) has so far overlooked its history as to tell u» "it 

 reached the first magnitude " ; and he attributes its discovery to 

 Kepler. 



The " AsTKONOMiscHE Nachrichten." — Contrary to what 

 has been lately stated, it appears that this periodical will still 

 be edited by Dr. C. F. W. Peters, who has for some time con- 

 ducted it, and we are informed there is a probability that Prof. 

 Kriiger may set afloat a new astronomical journal under his 

 own management. Wliether the multiplication of high-cla>s 

 astronomical journals to the extent we are likely to witness is a 

 practical advantage may perhaps be doubtful. For many years 

 the Astronomische Nachrichten contained almost all that bore 

 upon the progress of exact astronomy ; sed tempora muiantur, et 

 nos mntamur in illis. 



The Comet 1880 ^ (Swift, October 10). — The completion 

 of the mounting of the large Merz-Repsold refractor at the 

 Imperial Observatory, Strassburg, enabled Prof. Winnecke to 

 observe tliis interesting comet as late as January 26, when un- 

 favourable weather interfered, and be wa'^ not without the hope 

 that it would be within reach after the next period of absence oi 

 moonlight. Even if this should not prove to have been the case, 

 there will be more than fifteen weeks' observations available for 

 the determination of the actnal orbit of the comet, affording 

 every reason to expect that its track in the heavens nearly eleven 

 years hence, or at its next visible return, may be pretty closely 

 predicted. The following positions are deduced from MM. 

 Schulhof and Bossert's last elements : — 



At Greenwich midnight 

 1881. R.A, Decl. Log. distance from 



h. m. s . Earth. Sim. 



Feb. 14 ... 6 42 20 ...+21 21-4 ... 9-9007 ... 0-2147 



i6 ... 6 44 54 ... 21 10-4 ... 9-9158 ... 0-2192 



18 ... 6 47 29 ... 20 59-8 ... 99307 ... 0-2236 



20 ... 6 50 5 ... 20 49-7 ... 9'9454 ... 0-2280 



22 ... 6 52 41 ... 20 399 ... 9-9600 ... 0-2323 



24 ... 6 55 18 ...-I-20 304 ... 99745 ... 0-2366 



Prof. Winnecke reports that the Merz-Repsold refractor is a 

 great success ; Mimas is an easy object, and it may be hoiked 

 that the observation of the nebula;, to which it is understood the 

 instrument is to be chiefly directed, may not prevent attention 

 being given to the closest of Saturn's satellites. 



The Perseids in August, 1880. — M. BaiUaud, Director of 

 the Observatory of Toulouse, has published the results of the 

 watch for meteors, maintained by three observers on the nights 

 of August 9, 10, and II in the past year: 11 72 shooting-stars 

 were observed, and 83 of the longest tracks were traced upon a 

 chart ; generally the tracks were very short, and their extremities 

 pretty distant from the radiant. The meteors appeared to 

 diverge from two points — the more numerous group from R. .^. 

 42° 37', Decl. 56° 39'; and a group of about one third the former, 

 frooi R.A. 60° 39', Decl. 62° 4', The maximum; occurred on 

 August 10, between I4h. and ish., in which interval 200meteors 

 were noted. 



PHYSICAL NOTES 



M. Wiesnegg has lately constructed for M. d'Arsonval a new 

 steam-pressure regulator which deserves notice. It fulfill, 

 according to the inventor, the following conditions : — (l) It 

 maintains a perfectly constant pressure of steam in a boiler, 

 whatever the actual output ; (2) it maintains the consumption of 

 fuel at a rate proportional to the output of steam ; and (3) it is 

 absolutely automatic, and therefore prevents all risks of explosion. 

 This regulator is of very simple construction. A lead pipe from the 

 boiler leads to a little apparatus somewhat resembling an ordinary 

 lever safety-valve, but in which the valve-plug, instead of fitting 

 into tlie usual conical seat, rests upon a thin disk of india-rubber. 

 This disk rises when the pressure from below exceeds the down- 

 ward pressure of the plug and the superincumbent lever, and of 

 the weight which it carries. It cannot get h )t, as it is far from 

 the boiler, and the space below the disk is filled with water con- 



densed from the steam. The upper surface of the valve-plug 

 regulates by its movement the flow of gas, which comes in and 

 goes out by two pipes leading to the upper part of the regulator. 

 One of these comes from the gas mains, the other goes out to the 

 burners under the boiler. By this arrangement, whenever the 

 presmre in the boiler reaches any desired maximum, the apparatus 

 itself reduces the supply and turns down the flame, thus main- 

 taining the pressure constant .and the consumption proportional 

 to the output of vapour. It will be seen that the invention is 

 only applicable to the case where the fuel employed is gas. The 

 apparatus is also in itself an automatic safety-valve, putting out 

 the fire when the pressure exceeds the limit. M. Wiesnegg has 

 had practical experience during three ye.ars of the working of the 

 new regulator, which appears to leave nothing to be desired in 

 its performance. The same gentleman has constructed a constant- 

 pressure air-blast on the same principle. 



Prof. Cassani invites attention in the Rivista Sci. Ind. 

 (November 30) to some singular phenomena of geometrical 

 optics, thus indicated : — The real images, presented by a con- 

 cave mirror or by a convergent lens, of a plane or spherical 

 mirror, a lens or a prism, may by a suitable arrangement be 

 made to appear like a real mirror, lens, or prism respectively. 

 An observer stands opposite a concave mirror supported (with 

 slight slant) at a distance greater than the radius of curvature, 

 and receiving no other light than that reflected from his face 

 (illuminated by a dark lanterns). A small plane mirror s placed 

 in a position nearer the concave mirror than the observer, and 

 sloping in opposite direction (it is concealed from his eye). The 

 effect is that, on looking obliquely upwards, the observer seems 

 to see a plane mirror (which is of larger size than the other) with 

 his direct iii^age in it. The illusion is the more complete if the 

 actual plane mirror have an ornamental frame, and this be illu- 

 minated by a special lamp. As the image in the ideal mirror is 

 always rather small and too near the mirror, this may arouse 

 su.spicion, the more so when the image is seen to diminish on 

 receding and increase on advancing ; but a person not familiar 

 with the phenomena of concave mirrors may easily be deceived, 

 thinking he sees a real mirror. 



In the Froc. R.S.E. Sir W. Thomson describes a thermo- 

 magnetic thernioscope of an ingenious nature. It is well known 

 that the " permanent " magnetism of steel magnets is not 

 constan', but changes slightly with changes of temperature, the 

 magnet becoming weaker when warmed, and recovering its 

 strength as it is cooled. The magnetic therm iscope is intended 

 to indicate differences of temperature by showing differences 

 between the magnetic moments of steel magnets. Two thin 

 wires of hard steel, each one centimetre long, are arranged so as 

 to form a nearly astatic couple, being magnetised to equal 

 strength and set in oppo.-ite directions, but not quite parallel, so 

 that they set at right angles to the magnetic meridian. Two 

 other magnets, about twice the size of the former pair, are placed 

 one on each side of this astatic couple as "deflectors," being 

 laid in one line nearly along the magnetic meridian, with their 

 similar poles facing one another at about two centimetres apart. 

 When properly adjusted the little astatic pair suspended between 

 them will be found to be exce-sively sensitive to the least change 

 in the strength of either of the deflectors, and if they are at 

 different temperatures will turn through an angle which if small 

 may be regarded as a measure of the temperature-ditTerence. A 

 small mirror suspended from the lower needle of the pair serves 

 to reflect a sj ot of light on to a scale in the usual way. 



In 1870 and 1871 MM. Leverrier and Crova experimented 

 with an optical telegraph betv\een Nimes and Rede-san. Their 

 system of signals were made by means of oil lamps or petroleum 

 lamps fed by oxygen froai a supply that could be turned on or 

 off at will by an oj-erator, who thus produced intermittent 

 brilliant outbursts of flame according to a pre-arranged code. 

 During December, iSSo, a similar device %\as conceived by M. 

 Mercadier, against whom M. Crova now reclaims the essential 

 principles of his invention. He adds ihat two of the requisites 

 of siaccess lay in the use of oxygen under very low pressure, 

 feeding the flame by an orifice in the midst of the flame, and 

 in the employment of keys opeiiing and shutting the gas-passages 

 very suddenly by means of strong springs, without which the 

 changes in the intensity of the flame go on too slowly to be 

 Comfortably observed. In the experiments of 1S70-71 the lights 

 at Nimes were vi-ible at Redessan and vice versa, e\en in broad 

 daylight. The oxygen supply w-as contained in ordinary gas 

 bags of caoutchouc and prepared in the usual manner. 



