90 



NATURE 



[May 24, 1906 



habitation as possible. The charts show that the quantity 

 of chlorine near the coast amounts to 6 parts in a million, 

 at 4 miles away to 5 parts, at 20 miles to 3 parts, 

 at 40 miles to i part, and at 100 miles to 04 part. 



The fact that chlorine exists in rain water to a large 

 extent near the sea coast was stated in the report on 

 domestic water supply of the Rivers Pollution Commission 

 in 1S74. It was there shown that on the coast of Devon- 

 shire, where with south-west winds sea spray is blown over 

 the land, the amount of chlorine varies from 1-20 to 2.10 

 parts in 100,000, and at the Land's End, with a strong 

 south-west wind blowing, it amounts to as much as 21-8 

 parts. Inland the average quantity of chlorine diminishes to 

 039 part ; increases to 0-99 part at Liverpool and 0-79 part 

 at Newcastle. 



Paper No. 151, by Mr. Marshall O. Leighton, deals 

 with the field assay of water, and describes the methods 

 which have for some time been used in connection with the 

 investigations into the quality of water in various parts 

 of the United States. The methods described relate, not 

 to laboratory experiments, but to simple tests to ascertain 

 the general character of the water by methods which can 

 be carried out on the spot. These field determinations give 

 the turbidity and colour of the water, the presence of 

 chlorine, carbonates, calcium, and iron, and the amount 

 of hardness ; also the amount of suspendea matter. The 

 former are more particularly required in water for domestic 

 supply, and the latter for that used for irrigation purposes. 

 The amount of gradient to be given to a canal for con- 

 veying water for irrigation is governed to a great extent 

 by the solid matter in suspension, and this also affects 

 the capacity of the storage reservoirs. The method for 

 determining turbidity, accompanied by an illustration of the 

 gauge used for this purpose, was given in N.ature of 

 January 7, 1904. .\ description and illustration of the 

 Geological Survey field case is given in the paper. 



Paper No. 143, by Mr. J. H. Quinton, details the experi- 

 ments made under the direction of the Reclamation Depart- 

 ment on steel concrete pipes for the purpose of determining 

 the durability and permanence of these structures in con- 

 nection with the supply of water for irrigation purposes. 

 Thr> pipes experimented on were 5 feet in diameter, 20 feet 

 long, and 6 inches thick, of concrete, enclosing an armour 

 of steel rods sufficient to resist a head of 150 feet of water 

 with a factor of safety of 4. The experiments showed the 

 difficulty, even with the closest attention to the construc- 

 tion, of making pipes of this kind that would stand a head 

 of mo feet. 



Paper No. 150, by Mr. Robert E. Horton, gives the 

 results of an investigation of the theorv of weir measure- 

 ments, and the discharge over different forms of weirs. 

 The various coefficients of Bazin, Ftelev, Stearns, and 

 Hamilton Smith are analysed. A further description is 

 given of the experiments performed at the Cornell Uni- 

 versity laboratory, where a closely regulated volume of 

 water was passed over weirs of different forms placed 

 across an experimental canal, and the results obtained com- 

 pared with the different formula; for obtaining the dis- 

 charge. Tables are also given for calculating the discharge 

 over weirs. 



GREEN WICH ORSER VA TIONS. ' 

 T \ the introduction to the first work mentioned below, an 

 opinion is expressed that the revision of an old cata- 

 logue must always be a source of anxiety to those who 

 advise and undertake the revision, and that only the final 

 result can justify the expenditure of the time and labour. 

 Those who are responsible for this work need be under 

 no apprehension that their efforts have been misspent. It 



1 " New Reduction nf Groombridge's Circumpolar Calalojue f.ir the 

 Fpoch iSto-o." By F. W. Dyson. F. R.S., and W. G. Thackeray. Under 

 the direction of Sir William H. M. Christie, K.C.B., F.R.S., Astronomer- 

 Royal. (Published by order of the Board of Admiralty in obedience to 

 His Majesty's command. Edinburgh: Neill and Co., Ltd.. 1905.) Price 



" Telegraphic Determinations of Longitude made in th>- Years iSS8-jgo2 



under the direction of Sir W. H M.Christie, K.C.B.. F. R.S , Astronoiner- 



Koy.->l. (Published by the Board of Admiralty in obedience to His Majesty's 



Edinburgh: Neill^and Co., Ltd., 1906.) Price 15^. 



NO. 1908, VOL. 74] 



would rather seem that in this case they have fulfilled a 

 necessary duty, and discharged an honoured trust. It has 

 always seemed to the writer that the ancient authorities 

 at Greenwich were a little wanting in patriotism and 

 enterprise in entrusting to a foreigner, however eminent, 

 the reduction and discussion of Bradley's observations. 

 Groombridge's observations, in a sense, may not be so 

 completely a national possession as those of Bradley, but 

 certainly it is not unfitting that at the Royal Observatory, 

 almost within the shadow of which Groombridge erected 

 his transit circle, his observations should be examined and 

 discussed. 



There are several circumstances which tend to give dis- 

 tinction to Groombridge's work. At the beginning of the 

 last century his instrumental equipment was equal to, if 

 not more powerful than, that of any other observer in 

 Europe. The fact that, as an amateur, he gave his time 

 and leisure to the repetition of the same mechanical per- 

 formance shows that he was a lover of order and accuracy. 

 Pond, the Astronomer Ro}al, whatever his failings may 

 have been, appreciated the necessity for certainty and 

 accuracy, and he must have impressed these qualities upon 

 Groombridge. Further, the lapse of time, that factor 

 which has increased the value of so much astronomical 

 work and enhanced the reputation of so many worthies, 

 has fought on the side of the retired West Indian merchant. 



The method to be pursued in the reductions, how far 

 the observations are to be treated as independent, how far 

 they are to be regarded as differential, are points which 

 must be left to the decision of the computers. They must 

 accept the entire responsibility, since the knowledge and 

 experience is theirs. In this case it is not impossible but 

 that they have had the assistance of tradition. The 

 interesting remarks of Colonel Colby and Dr. Firminger 

 quoted by the revisers, probably do not exhaust the inform- 

 ation at their disposal. It would be an impertinence for 

 anyone who has not even seen the originals to offer any 

 criticism on the methods einployed by those who have 

 gained familiarity and experience by long contact with 

 Groombridge's figures. These methods are described with 

 clearness and in sufficient detail, but the revisers must 

 know so much more than they can set down. 



The result is to obtain a catalogue for the equinox of 

 1810 of 4239 stars. The number in the original Groom- 

 bridge catalogue was 4243, but of these nine have been 

 rejected on various grounds, and five have been added as 

 separate stars. The places of a few more stars have been 

 considered discordant, and have not been used in the sub- 

 sequeiit discussion of proper motion. The accuracy of the 

 catalogue and the care of the observer can both be estimated 

 in some measure from the fact that a discrepancy of four 

 seconds of arc in either right ascension or polar distance 

 has been considered a proper limit to warrant the exclusion 

 of the observation. The number excluded is 75 in right 

 ascension and 214 in polar distance, slightly more than 

 I per cent, of the total number of observations. 



The peculiar value of this catalogue lies in the fact that 

 its epoch is 1810. Therefore, by comparison with modern 

 observations, it offers the means for a new determination 

 of the precessional constant, while the new proper motions 

 which it makes available should give greater certainty to 

 researches into the amount and direction of the solar 

 motion. The length of time elapsed since Groombridge's 

 day is not much less than that available in the case of 

 Auwers-Bradley, and the accuracy of the observations would 

 seem to be of the same order; but Bradley's optical means 

 were smaller, and the average of his stars considerably 

 brighter. Groombridge's stars include many of the ninth 

 magnitude, and fill a gap between those to which Bradley's 

 observations refer and the results that will be derived from 

 photography. On the other hand, Bradley's stars were 

 better distributed over the whole sky. Groombridge limited 

 his observations to the circumpolar regions. Against this 

 drawback, as against many others, the Greenwich authori- 

 ties have struggled with apparent success, and a few of 

 their final results may be given. 



We have, in the first place, the proper motions of more 

 than four thousand stars determined by comparison of 

 places at intervals of approximately ninety years. These 

 proper motions have been derived for the most part by a 



