SCIENCE. 



129 



Mr. J. H. Stebbins, Jr., called the attention of the 

 society to several new coloring materials that he had 

 discovered among the di-amido compounds. They were 

 yellow in color and suitable for silk, woolen and cotton 

 dyeing, but especially desirable tor the latter. 



Dr. A. R. Leeds gave a short description of some new 

 experiments on the action of hydrogen peroxide with 

 ammonium hydrate. 



A committee consisting of Mr. Casamajor and Dr. 

 Alsberg were appointed to make arrangements for the 

 annual dinner. M. B. 



New York, March 9, 1881. 



IMPROVED PORTABLE EQUATORIAL STANDS. 



By James H. Gardiner. 



The stand I use, and those which I have seen, have no 

 levels and no means by which the telescope can be moved 

 in azimuth without moving the whole stand. It seems 

 to me that, with a very little trouble, these stands 

 could be made not only a great deal more accurate, but 

 also much more useful for amateur work by the following 

 additions : Instead of having the equatorial mounting 

 screwed firmly to the lower plate to which the legs are 

 attached so the telescope cannot be moved in azimuth 

 without moving the whole stand, a plate could be ground 

 to touch, say, only % of an inch, and revolved on the 

 lower plate. This would give a steadier and easier motion, 

 with less friction than if the two plates were ground to 

 touch all over. A thread is to be cut in the side of this 

 upper plate, so that with a tangent screw it can be 

 moved in azimuth. On this upper plate that revolves on 

 the lower plate, and to which the tangent screw is attached, 

 should be placed two levels at right angles to each other, 

 and then on this upper plate that revolves the usual equa- 

 torial mounting is to be firmly fastened. Ii will be seen 

 that the above stand only differs from the usual stands on 

 tripods, in having levels and means to move the telescope 

 in azimuth without moving the whole stand. Such 

 a stand would be of great use to amateurs, who have a 

 poor horizon, and are obliged to move their stands about 

 to command all parts of the heavens ; or for those who 

 may have a good horizon, but cannot afford the luxury of 

 a fixed pillar and dome. The use of such a stand will 

 appear from the following illustration ; Suppose the ob- 

 server has such a stand, and that he is at Washington, 

 and on ihe 1st of March, 8 P. M., he desires to put his 

 telescope in the meridian. He carefully levels the stand, 

 and turns his telescope on a Polaris to come into the 

 centre of the field. If it does not happen to come exactly 

 in the centre of the field, he can raise or lower his polar 

 axis, or move the telescope in azimuth by aid of the tan- 

 gent screw. Here it is to be noted that with the old 

 stands he would have to twist the whole stand around and 

 throw it out of level, and by repeated trials get a Polaris in 

 the centre of the field, and when he again levelled the 

 stand a Polaris might not be in the centre of the field. 

 Thus every movement of the old stand would throw it out 

 of level. All these tedious trials are obviated by the new 

 stand with azimuth motion. When once levelled it would 

 stay so, and the telescope could be moved to the east or 

 west without having to be continually bothered with 

 levelling it. Thus in a few moments he would have a 

 Polaris in the centre of the field, and the telescope 

 approximately in the meridian. He now reads his R. A. 

 circle, and turns his telescope on some well known star, 

 as a Leonis or Regains, for example, and then reads his 

 R. A. circle again. Supposing the difference of these two 

 readings of the R. A. circle to be 3h. 25m. 13s., this is the 

 observed hour-angle of Regulus. The true hour-angle of 

 Regulus is equal to the difference of the Sidereal time and 

 the R. A. of Regulus, or 3)1. 22m. 13s. This shows that 

 the object-end of the telescope must be moved 3m. to the 

 west to make the observed hour-angle agree with the true 



hour-angle. This can be done nicely by the targent screw 

 that moves the telescope in azimuth without throwing it 

 out of level, but with the old kind of stand it would be 

 thrown out of level, and it would be a very tedious job, 

 requiring time and patience to accomplish. Having got 

 the telescope very nearly in the meridian, the declination 

 circle can now be set to the <5 of the star. With such a 

 sand the careful amateur can put it near enough in the. 

 meridian to pick up a comet or any other object by its R. A 

 and 5. The accuracy of the adjustments depends upon 

 the levelling, the collimation, and an exact value of the 

 local time. The levelling would generally be accurate 

 enough, and most stands have screws in the saddle 

 that carries the telescope for correcting the collimation. 

 But the amateur should try to get the exact value of his 

 local time, as this would probably introduce the greatest 

 error. This can be done by equal altitudes of the sun or 

 star. Or where the latitude of the place is well known the 

 local time may be found by an altitude of the sun. With 

 such a stand as has been described, if it should be necessary 

 to move it to another place, it could easily be put in the 

 meridian again, as described. Besides, many have stands 

 with good circles which they seldom use, because they 

 cannot afford a fixed pillar and dome, and do not care to 

 put it in the meridian, as they are obliged each night to 

 bring the telescope into the house. But if it could be put 

 in the meridian easily, I am sure many would be pleased 

 to use their circles. 



ASTRONOMICAL MEMORANDA. 



[Approximately computed for Washington, D. C, Monday, 

 March 21, 1881.] 



Sidereal time of mean noon, 23 h , 57™, 24 s . Equation 

 of time, 7 m , 8". Mean noon preceding apparent noon. 



On the morning of March 20th, the sun crosses the 

 equator and enters the constellation Aries, thus indicat- 

 ing the commencement of Spring. The violent actions 

 upon the sun's surface have continued throughout the 

 past month. 



The moon reaches its last quarter on March 22, and is 

 new again on the 29th. On March 21st, she crosses the 

 meridian at 4 A. M. The moon will be in conjunction 

 with Mercury on the 27th, and with Jupiter and Saturn 

 on the morning of the 31st. 



Mercury is morning star, crossing the meridian about 

 an hour before the sun, nearly 6 degrees farther south. 

 Mercury was in inferior conjunction with the sun on the 

 nth and is travelling towards the west. 



Venus has been moving westward since her greatest 

 eastern elongation on the 20th of February, and willcon- 

 *inue to increase in brilliancy till March 27th. She 

 crosses the meridian at about 2.40 P. M., about 20 degrees 

 farther north than the sun. 



Mars, crossing the meridian nearly 3 hours in advance 

 of the sun, is coming towards us, and gradually increasing 

 in brilliancy. 



Jupiter crosses the meridian at about 1.15 P. M., and 

 Saturn 15 minutes later. They are both becoming very 

 unfavorably situated for observation, and must be looked 

 for immediately after sun-set. 



Uranus is in right ascension io h , 50'", 47 s ; declination 

 8° 14' north, and was in opposition on March 1st. 



Neptune, right ascension 2 h , 47" 1 , 17 s ; declination 13° 

 56' north. Neptune and Venus are in conjunction on the 

 23rd. 



THE following is a list of the officers and council of the 

 Royal Astronomical Society, elected February ii, 1881 : — 

 President : J. R. Hind ; Vice-Presidents : Prof. Cayley, E, 

 Dunkin, W. Huggins, E. J. Stone ; Treasurer : F. Barrow; 

 Secretaries: W. H. M. Cnristie. J. W. Glaisher ; Foreign 

 Secretary : the Earl of Crawford ; Council : Prof. Adams, 



