426 



NATURE 



[September i, 1892 



briefly, and in a general way, the character of the data on 

 which the results depend. 



The objective of the transit instrument with which these ob- 

 servations were made, had a focal length of 8 feet and 6 inches 

 and a diameter of 5*85 inches. It was so constructed that the 

 ocular and the objective could be interchanged. It was also re- 

 versible, and a part of the observations were made with the 

 clamp east and the remainder with the clamp west. This con- 

 struction permitted the observations to be made under four 

 different sets of conditions, and for that reason the observed right 

 ascensions of each star were arranged, for facility of discussion, 

 in four separate groups. 



An examination of the results in each group discloses some 

 interesting facts that are worth considering somewhat in detail. 

 The whole number of stars in the catalogue that are reckoned 

 as standard stars, and are south of 70° north declination, is 365. 

 Of this number 70 per cent, have a range, in the individual 

 results, in at least one of the four groups, of two-tenths, orrliore, 

 of a second of time. This range is between 0*20 and 029 for 

 142 stars ; between 0*30 and 0-39 for 92 stars ; between 0-40 and 

 0'49 for 15 stars ; and 0*50 or more for six stars. The mean 

 range for the 255 stars is 0-297. In general, the accordance be- 

 tween the individual results is quite good, but the discordance 

 just mentioned sometimes occurs more than once in the collected 

 observations of the same star, and these doubtful data have been 

 used in deducing the standard places given in the catalogue. It 

 is not necessary to look for minor discrepancies, for enough of 

 appreciable magnitude have been cited already to warrant the 

 conclusion that better observing can and ought to be done with 

 modern instruments, and that the needs of astronomical science 

 to-day demand a more comprehensive, and a more accurate, 

 standard catalogue of right ascensions. 



These remarks must not be interpreted as unfavourable criti- 

 cism of the Pulkowa Catalogue, by far the best work of its period, 

 but they are made simply to call attention to the fact that the 

 present state of stellar astronomy and the direction which the 

 investigations of the immediate future are likely to take, plainly 

 require the most accurate fundamental catalogue of the standard 

 stars that modern instruments and appliances, modern methods 

 and the most skilful observers can produce. All of these con- 

 ditions are essential, and they must be carefully co-ordinated 

 to obtain the desired results. 



It must be plain to every astronomer that the needed funda- 

 mental catalogue must be deduced from new observations. The 

 reduction and the discussion of old observations of doubtful quality 

 is a waste of time and energy. Under existing circumstances 

 the greatest weight must be given to the observations. Neither 

 amount of labour nor skill in computation can derive results of 

 the desired accuracy from careless, incomplete, or incorrect ob- 

 servations. An attempt on the part of the computer to apply 

 any system of theoretical weights, either simple or complex, to 

 such observations is almost certain to lead, at least, to self-de- 

 ception ; and the safe as well as reasonable rule in such case 

 would be to use the weight zero. 



One example may serve to illustrate the effect of dealing con- 

 tinuously with old observations. In standard star positions the 

 four principal national ephemerides are not only not in accord 

 with each other, but they generally do not exhibit results even 

 from the few best modern observations. The many discrepancies 

 of varying magnitude in these volumes present with marked 

 emphasis the undesirable results arising from the custom of 

 " threshing old straw." 



The data on which these several ephemerides are founded are 

 the common property of all astronomers, and no one can claim 

 the exclusive use of any published observations ; and yet national 

 pride or national obstinacy, which is sometimes mistaken for 

 the nobler sentiment, or some computer's pet scheme or system 

 of combination, has led to the adoption of a variety of assump- 

 tions in the interpretation and treatment of the original data 

 until our standard ephemerides are so complex in their structure 

 that the exact details of their preparation are practically unknown 

 outside their respective computing offices. The accuracy of the 

 star positions is unchecked by any recent fundamental observa- 

 tions, and they lack that trustworthy character that should inhere 

 in a system intended to serve as a basis for even good differential 

 work. 



If this character were wholly satisfactory, we should soon see 

 the representatives of astronomy, geodesy, and geology gather- 

 ing about the zenith telescope, confident of reaching some definite 

 conclusion in regard to the variation of terrestrial latitudes by 



NO I 192, VOL. 46] 



the systematic use of this simple instrument. But the accurate 

 star positions do not exist, and under the present conditions the 

 most feasible plan for utilizing this instrument is to so arrange 

 the observing stations as to eliminate the effect of errors in the 

 star places. 



If it be admitted that sidereal astronomy is worthy of further 

 and more accurate study, that the needs of astronomical research 

 at the present time and in the immediate future demand more 

 exact positions of the standard stars, it may be desirable to con- 

 sider briefly the status of those agencies to which we must look for 

 the successful prosecution of such an investigation. 



It is not an easy task to determine the exact number of active 

 observatories in the world. Some published lists contain the 

 names of all observatories, from the most expensive and fully 

 equipped Government establishments to the temporary shelter 

 that protects a small equatorial telescope^ and perhaps a chrono- 

 meter, which is kept by the owner for the amusement and pos- 

 sibly for the instruction of himself and his friends. A fair 

 enumeration, however, would probably give a list of about 

 250 observatories sufficiently equipped to do some kinds of astro- 

 nomical work. Of this number more than 20 per cent, are found 

 in North America. In the equipment of these 250 observatories 

 are to be found about sixty transit circles with objectives 

 ranging from nine to about three inches. The quality 

 of about one-fourth of these instruments is such that 

 good results may be expected from their proper employ- 

 ment. To the latter class of instruments we are limited 

 when we seek for the highest class of work now under con- 

 sideration. If we take account of the modern subsidiary 

 apparatus, and of the electric methods of recording transit 

 observations and illuminating the different parts of the instru- 

 ment, it does not seem extravagant to conclude that, if one third 

 of the best transit circles were devoted for the next four years 

 to observations for the formation of a fundamental star catalogue 

 of right ascensions and north-polar distances, the aggregate 

 result would be not only the best positions ever published, but 

 it would be of the greatest value in the discussion of current, 

 as well as future, astronomical problems. Unfortunately, how- 

 ever, we do not find any such number of instruments employed 

 in fundamental work. At the present time there is no general 

 fundamental work in progress in any portion of the world, and 

 within the last thirty years there have been no results of that 

 character to take the place of the Pulkowa determinations. 

 This statement does not refer to observations of one ordinate 

 only, or to those cases where seVeral observers, both trained 

 and untrained, are accustomed to observe in turn with the same 

 instrument and their several results are indiscriminately mingled 

 in such a way that critical discussion is out of the question. 

 Several observers may work together in the determination of 

 declinations with a fair degree of success, because, to a large 

 extent, each observer's work in a period of twelve or twenty- 

 four hours is independent of that of his fellow's ; but even this 

 work is better when done by one skilled observer alone. 

 Fundamental right ascensions, however, cannot be determined 

 with the requisite accuracy, and the necessary freedom from 

 systematic errors, if more than one or, at most, two observers 

 work with the same instrument. If only accidental errors of 

 observation, or such as are due to atmospheric disturbances, 

 uncomfortable positions, or the unsteady nerves of the observer, 

 were introduced by increasing the number of observers, then 

 increasing the number of obstrvations would tend to diminish 

 the error of the result. But the personal errors of observers, 

 and their various habits of manipulation, are of the same nature 

 as systematic errors, and cannot be eliminated by increasing the 

 list of observers or the number of observations. 



Of the many valuable star catalogues in existence, I know of 

 none in which the right ascensions depend upon the observations 

 of more than one astronomer, where it is possible to know, or 

 to eliminate, either the constant or the variable errors due to the 

 personal equation of the observers. 



In the current astronomical work of this country in which we, 

 as members of this section, are especially interested, observations 

 and discussions, planned solely, and properly carried out, for the 

 determination of absolute star places, are quite unknown. The 

 necessary instrumental outfit, with the exception in some cases 

 of a clock of the requisite quality, exists in several observatories, 

 and I have no doubt that trained observers of the highest 

 character can be found to meet all demands. 



With the exception of a few Government establishments, and 

 of those built to promote a higher grade of instruction, the ob- 



