374 



SCIENCE. 



the right amount. All that is more or less than the exact 

 amount required, reduces the temperature so much. 



In ordinary furnaces, it has been estimated that much 

 more than half the heat is lost by this one item alone. If 

 the air passes freely in above the coal, twice as much goes 

 in as is burned ; if it all passes in under the grate, then 

 only one-third the heat is given off, as only carbonic oxide 

 escapes. 



Probably the advantages with crude petroleum or 

 with coal, of the water process, would be of still greater 

 value.* 



Samuel J. Wallace. 



Washington, D. C. 



BOOKS RECEIVED. 



Observations of Double Stars made at the United 



States Naval Observatory by Asaph Hall, Professor 



of Mathematics, U. S. N. Rear Admiral Rogers, U. 



S. N., Superintendent, Washington, 1 88 1 . 



In introducing this work Professor Hall gives some 

 very interesting details respecting the methods used in 

 making observations at the Naval Observatory and the 

 condition of the instruments. 



He also presents his reasons for undertaking these ob- 

 servations and indicates the scope of the present work. 



He states that his regular observations with the 26- 

 inch refractor of the Naval Observatory were begun in 

 the spring of 1875, the instrument at that time being in 

 charge of Professor Simon Newcomb. " Professor New- 

 comb gradually withdrew from observing with this in- 

 strument, which came under my direction sometime in 

 July of the same year. The micrometrical measure- 

 ments which had been made by Professors Newcomb 

 and Holden were chiefly of the satellites of Uranus and 

 Neptune, and the discussion of these measurements of 

 the two outer satellites of Uranus brought out very 

 clearly what had been indicated before by Von Asten ; 

 viz, the existence of a large constant difference in the 

 angles of position measured by Mr. Otto Struve, director 

 of the Imperial Observatory at Pulkovva. As it is our in- 

 tention to repeat the measurements of the satellites of 

 Uranus and Neptune after a few years, and as it seemed 

 probable that similar differences might exist in the obser- 

 vations of double stars, it occutred to me that the best 

 way of comparing and uniting the observations of differ- 

 ent astronomers would be for each one to observe the 

 same double stars at nearly the same time. I wrote to 

 Struve proposing that this should be done, and that he 

 should select the list of stars. In reply he informed me 

 that such a series of observations was already in progress 

 between himself and Baron Dembowski, and alter adding 

 to the list of stars a few of greater distances, this list and 

 an account of the proposed work were published by 

 Struve in the " Vierteljahrsschrift der Astronomischen 

 Gesellschaft." Band xi, p. 227.+ 



It was understood that each observer should avoid all 

 knowledge of the observations of other astronomers, in 

 order that his work might be done independently, and in 

 my own case this rule has been carefully adhered to. But 

 now nearly four years have elapsed since Struve's publica- 

 tion, and it is probable that all the astronomers engaged 

 in this work have collected such a number of observa- 

 tions that the publ cation of my own results will not in- 

 fluence the independence of theirs. Moreover, the end 

 of the year 1879 seems to be a favorable epoch for pub- 

 lishing my observations of double stars made before 1880, 



♦This superiority of the non-luminous combustion for heating was 

 discovered hv 1'rofessor Henry. He says : " With this arrangement the 

 light of the flame was increased, while the time of bringing the water to 

 the boiling point was also commensurably increased, thus conclusively 

 showing that the increase of light was at the expense of the diminution 

 of the temperature." 



t Mittheilung liber untcrnommene Beobachtungsreihen zur Verglei- 

 chuDg von Mikrometer messungen. 1876, Anfang Juni. Otto Stkuve. 



since I hope to make some changes which in the future 

 will enable me to observe under conditions more favor- 

 able to accuracy. 



I have therefore collected and revised all my observa- 

 tions of double stars, and the results are given in the 

 following pages. In order to make this collection com- 

 plete I have concluded the few observations made in the 

 year 1863 with the equatorial of 9.6 inches aperture. 

 The whole number of observations is 1614. 



It will not be necessary to give any general description 

 of the 26-inch refractor made by Alvan Clark and Sons 

 for the Naval Observatory, since such descriptions can be 

 found in the annual volumes of the Observatory for 1873 

 and 1874. It will be sufficient to say that the form of 

 the mounting adopted by the makers for this Equatorial 

 is such that the instrument, notwithstanding its great 

 size, is handled with ease ; and the harp-shaped piece that 

 supports the polar axis is very convenient when observing 

 near the zenith. Generally the instrument is pointed on 

 a star by means of what are called the " rough circles." 

 These circles are the edges of the hour and declina'ion 

 circles, which were painted white, and then divided by 

 lines of black paint, the hour circle into spaces of ten 

 minutes of time and the declination circle into degrees. 

 This method of pointing is usually accurate enough to 

 find the object, but as the painting was not well done 

 errors as great as 15' to 20' could be made in some parts 

 of the rough declination circle. An accurate reading for 

 the position could be made by means of the finely divi- 

 ded circles, but this involves considerable time and 

 trouble. On account of the delay in the observations 

 which would be caused in making the change, and of the 

 natural inertia in getting rid of a poor thing to which one 

 has become accustomed, this defective circle for the de- 

 clination was used until June, 1879, when the circle was 

 painted white and divided again under the care of Mr. 

 Gardner, the instrument maker of the Observatory. The 

 settings are now much more accurate and give but little 

 trouble, and the saving of time is very great. It is pos- 

 sible that a few cases may be found where, on account 

 of an erroneous setting in declination, I have observed a 

 different object from the one supposed. 



The ease and rapidity with which observations can be 

 made with a filar micrometer depend largely on the per- 

 formance of the driving-clock. The accuracy of the ob- 

 servations also is in a measure dependent on this per- 

 formance, but patience and skill on the part of the ob- 

 server will in a good degree make up for a poor perform- 

 ance of the clock. The motive power of our driving- 

 clock comes from a small water-wheel which is driven 

 by water drawn from the Potomac water pipes. At first 

 the water was applied directly to the conical pendulum, 

 but the pressure of the water was so variable that weights 

 attached to an endless cord (Huygen's loop), were placed 

 between the water-wheel and the pendulum by Professor 

 Newcomb. When this had been done the performance 

 of the clock is said to have been tolerable ; but in the 

 autumn of 1875 it became very troublesome, and the ob- 

 server was frequently annoyed by the stopping of the 

 clock. This trouble continued and became worse until 

 July, 1S76, when the clock was dismounted by Mr. Gard- 

 ner and myself. The lower end of the shaft of the con- 

 ical pendulum had been given a conical shape, and 

 had rested in a conical cup. The friction and heat 

 had been so great that the lower end of this shaft 

 had become very rough and twisted to a gimlet 

 shape, thus stopping the clock. The bearing of the shaft 

 was changed and made of a plane agate surface, the 

 lower end of the shaft being rounded to a slightly curved 

 surface. The friction of the upright shaft of the water- 

 wheel was also diminished by clamping a set of friction 

 wheels to this shaft and letting them play on a horizontal 

 iron surface. The weights on the Huygen's loop were 

 changed for cups carrying shot. With an average pres- 

 sure of the water, and the machinery well oiled, these 



