54 



NA TURE 



[May 19, 1887 



theory, ifweinteni to grapple with every kind of proposition 

 we require a threefold division. We must be able to show that 

 a compartment is empty, that it is occupied, or that we do not 

 know what is its state. 



Speaking only of diagrammatic illustration, since it is to this 

 that Mr. Sidgwick is referring, I may say that I have indicated 

 in an article in Mind (1883, p. 599) how such a threefold 

 scheme of alternatives could be displayed. Reference to this 

 will be found also in Mr. Keynes's " Formal Logic." 



I cannot ask for space to discuss the subject fully here. But 

 I would remark that any scheme that confines itself to two 

 alternatives seems to me to be necessarily open to one or other 

 of two serious drawbacks. Either (r) we have to assume that the 

 assertion of a proposition carries with it the existence of its 

 subject. This begins plausibly enough ; but when fully worked 

 out it forces us to abandon various universally recognized rules, 

 such as some of those for conversion, contraposition, &c. It 

 also, in the case of complex propositions, departs even further 

 from convention than the opposite doctrine does. And it 

 wholly fails to express hypothetical propositions. I have pointed 

 out these difficulties in my " Symbolic Logic," and the first of 

 them will be found very fully treated by Mr. Keynes. Or (2) 

 we may reject the assumption just mentioned, as Boole and 

 Jevons practically do. We are then wholly unable (in spite of 

 the attempts made by each of these writers) to express particular 

 propositions. John Venn. 



Cambridge. 



THE PARIS ASTRONOMICAL CONGRESS. 



T N our last article we brought down our reference to the 

 -»■ proces-verbaiix as follows ; — General Congress meeting, 

 April 19 ; Photographic Committee meetings, April 20 

 and 21 ; Astronomical Committee meetings on the 20th, 

 2 1st, and 22nd. We have since then received from 

 Admiral Mouchez the following records : — Third and 

 fourth meetings of the Congress on the 23rd and 25th; 

 meeting of the Permanent Committee on the 26th ; and 

 meeting of the Permanent Bureau on the 27th. The two 

 final meetings of the Congress were held chiefly to receive 

 the reports of the Astronomical and Photographic Sub- 

 Committees which have been appointed, and to whose 

 proceedings we have referred in detail, and also to 

 appoint a Permanent Committee, and if necessary a 

 Bureau. 



It will be convenient, then, that we should commence by 

 referring to the third and fourth general meetings held on 

 the 23rd and 25th. This first meeting considered the 

 various resolutions which had been arrived at by the Sub- 

 Committees, and the discussions upon them do not appear 

 to call for any more remarks upon our part. With regard 

 to the construction of the object-glass for the light near 

 G, the eminent optician, Steinheil, communicated a note 

 which will appear among the records of the Congress, but 

 of which no details are given in the prods-verbal. With 

 regard to the supplementary negatives which are to be 

 obtained for purposes of a catalogue of the stars of refer- 

 ence, the Astronomer-Royal was evidently under the 

 impression that to endeavour to obtain stars of the 

 eleventh magnitude might be going a little too far, and he 

 therefore proposed that a resolution should give authority 

 to the Permanent Commmittee to determine down to 

 what magnitude, not beyond the eleventh, these photo- 

 graphs should include. The Astronomer-Royal also was 

 evidently under the impression that the Congress had 

 been called together to obtain a photographic autobio- 

 graphy or map of the heavens in this present century 

 chiefly, and that it should not lay so much stress as the 

 astronomers present were inclined to do upon a mere 

 catalogue. 



Mr. Gill, Her Majesty's Astronomer at the Cape, seems 

 to be of a different opinion, as he remarked that it is 

 necessary to make a catalogue if the thing is possible. 

 The number of stars to appear in the catalogue if the 

 eleventh magnitude is adopted will be about 1,500,000 



according to M. Paul Henry, and according to Dr. 

 Schoenfeld, if the 11-5 magnitude were adopted no less 

 than 3,500,000 stars. Subsequently the matter was put to 

 the vote, and the resolution as it came down from the 

 Astronomical Section was approved, Mr. Christie's 

 amendment being lost. 



The Congress next passed on to consider the distribu- 

 tion of work among the different Observatories. MM. 

 Beuf and Cruls, representing the Observatories of La 

 Plata and Brazil, were the first to reply that they 

 were ready, it being understood that the price of a tele- 

 scope similar to that employed by the Brothers Henry 

 would be something like 40,000 francs. Admiral Mouchez 

 stated that it had been decided that the Obseivatories of 

 Algiers, Bordeaux, Paris, and Toulouse would represent 

 the part which the French Government would be pre- 

 pared to take, and he also stated that in all probability 

 the Observatory of Santiago in Chili could undertake 

 some portion of the work. M. Weiss stated that the 

 participation of the Vienna Observatory might be regarded 

 as certain. MM. Tacchini and Oom, representing the 

 Observatories of Rome and Lisbon, had little doubt 

 that their Governments would furnish the requisite sums. 

 M. Duner stated that the Senate of the University of 

 Helsingfors would contribute a photographic refractor, and 

 he did not anticipate any difficulty with his Government. 

 M. Struve had no instructions ; M. Auwers was in the 

 same case ; Messrs. Christie and Gill followed suit. Mr. 

 Russell declared that in his opinion the necessary funds 

 would be provided to enable the co-operation ^f the 

 Observatories of Melbourne and Sydney to be assured. 

 Mr. Peters said that he had no doubt that there would be 

 ten Observatories in America anxious to help in the work, 

 but he did not know if they would accept all the terms 

 and conditions of the resolutions of the Congress. M. 

 Pujazon, representing Cadiz, thought that he could 

 promise assistance towards the map, but he could 

 promise nothing relating to the catalogue. 



M. Foil, representing Brussels, then proposed the fol- 

 lowing resolution : — 



" If an astronomer takes, by means of a telescope 

 different to that suggested by the Committee, photographs 

 which fulfil the conditions laid down for the map, he 

 shall be able, with the concurrence of the Permanent 

 Committee, to join in the execution of it." 



This was subsequently withdrawn. 



The final meeting of the Congress was held on the 25th, 

 and the point first discussed was that relating to the 

 Permanent Committee. M. Knobel proposed, on behalf 

 of some of the French astronomers, the following 

 resolution : — 



"That there should be two categories of members 

 in the Permanent Committee— first, the Directors of 

 Observatories where the work is carried on ; and 

 secondly, others not necessarily taking part in the con- 

 struction of the map. This Permanent Committee should 

 name its own Bureau, consisting of a President, two Vice- 

 Presidents, and two Secretaries." 



Next followed a discussion as to the number of 

 members of which the Committee should consist. A 

 considerable difference of opinion was made manifest by 

 the remarks of many members of the Committee, a.nd 

 Admiral Mouchez, with the apparent intention of coming 

 to an agreement, proposed the following series of resolu- 

 tions : — 



(i) "Before separating, the International Congress 

 shall delegate its powers to a Commission of eleven 

 members, forming an Executive Commission, charged to 

 study all the questions which have been referred to, and 

 to hasten the preparations for the execution of the map 

 as much as possible. The Directors of Observatories 



