SCIENCE. 



579 



nity, and also the degree of visability of these granula- 

 tions during the transit. 



Article 2. — It will be well to employ a reflecting 

 prism, or a polariscopic eye piece, to diminish the heat 

 and consequent danger to the observer's eyes. 



If it be decided to use a silvered objective, a method 

 which offers the great advantage of eliminating all the 

 obscure heat rays and doing away with errors from dis- 

 tortion arising from heating of the interior of the tube, 

 the excess ot light may be absorbed by a neutral tint 

 glass composed of two glasses of similar thickness, one 

 being colored and the other colorless. 



Article 3. — The eye-pieces should be positive, achro- 

 matic, and ot a power of 150. The observations of con- 

 tacts should be made in a field sufficiently clear to show 

 plainly projected on the solar disc, two wires separated 

 by a distance of 1". 



Means should be employed to remove as far as possible 

 the effects of atmospheric dispersion. 



The setting point of the reticule should be previously 

 ascertained on the stars or by means of a collimator 

 focussed to stars. 



In cases ot observation by projection, correspondent 

 means should be employed. 



Article 4. — The times corresponding to internal con- 

 tacts may be defined as follows : 



Ingress. The moment when an evident and, at the 

 same time, persistant discontinuity in the illumination of 

 the apparent limb of the sun joining the point of contact 

 with Venus, disappears. 



Egress. The moment of the first appearance of an 

 evident and, at the same time, persistent discontinuity in 

 the illumination of the solar limb joining the point of con- 

 tact. 



If the limb of two stars coming into geometrical con- 

 tact, without obscuration or deformation of the inter- 

 posed thread of light, the instant previously defined is 

 that of contact. 



If there be produced a black drop or ligament, well 

 defined and as dark as the body of the planet, the pre- 

 cedingly defined instants, are for Ingress, that of definite 

 rupture, and for Egress, that of the first apparition of the 

 ligament. 



Between these two extreme cases, other appearances 

 may be produced when the instants of contact may be 

 noted as follows : 



If the limbs remaining without deformation, there is 

 produced an obscuration of the luminous thread, with- 

 out the shadow, however, being as dark as the body of 

 the planet, the observer notes the instant of geomet- 

 rical contact. The moment of the formation or disap- 

 pearance of this shadow should also be noted. 



If the shadow is almost or becomes quite as dark as 

 the, planet, the precedingly defined instant is that when 

 this equality ceases or is established. 



The observer should also note whether there is pro- 

 duced on the luminous thread, any fringes or any other 

 distinct phenomena, and should note the moment of their 

 appearance and disappearance. 



It is generally desirable to note the time of occurrence 

 of any distinct phenomena about the time of contact. 

 Nevertheless it is a grave mistake, and one that should 

 be guarded against, to multiply the noting of times near 

 the occurrence of a contact. 



The time of appearance of phenomena of a distinct 

 character, should be mentioned only in such a manner as 

 to be readily separated from other phenomena observed 

 about contact. 



It will be useful in all cases that the observer should 

 illustrate his notes with a drawing made immediately 

 after each complete observation of contact, in order to 

 show more clearly the interpretation which he attaches 

 to his description of the phenomena. 



ARTICLE 5. — As the limb of Venus falls internally on 

 the solar disc during internal contact, as has been noted 



in Article 4, the observer should indicate as closely as 

 possible whether the moment when the limbs of Venus 

 and the sun, apparently coinciding, seem to be length- 

 ened out. 



This observation, though rough, is still desirable as a 

 check to the principal noted phase. 



Article 6. — Notwithstanding the fact that observa- 

 tions of external contacts are subject to considerable 

 uncertainty, the conference recommends that they be 

 observed either by direct vision or by means of the spec- 

 troscope, and that the point on the solar disc, where the 

 first contact takes place, be determined in an appropriate 

 manner. 



Comptes Rendus, Oct. 17, 1881, t xciii., p. 569. 



BACTERIAN NOTES. 



So long as the makers of microscopes do not place 

 at our disposal much higher powers, and as far as possi- 

 ble without immersion, we shall find ourselves in the do- 

 main of the Bacteria, in the situation of a traveler who 

 wanders in an unknown country at the hour of twilight, 

 at the moment when the light of day no longer suffices 

 to enable him clearly to distinguish objects, and when he 

 is conscious that, notwithstanding all his precautions, he 

 is liable to lose his way. — Cohn. 



Bacteria were regarded as animals up to the time of 

 Dujardin ( 1841 ), a kingdom — the Protista — midway be- 

 tween the animal and vegetable, being created by Haeckel 

 for their especial benefit. Duvaine ( 1859 ) was, however, 

 among the first to show clearly their alliance with the 

 alga;. Cohn holds them to belong to the algse, although 

 from warn of Chlorophyle, approaching the fungi. Mag- 

 nin says, " If there are still some differences of opinion 

 among naturalists as to the place of the Bacteria among 

 the cryptograms, there is but one opinion of their vege- 

 table nature." Sachs, however, solves the difficulty by 

 uniting the alga? and fungi in a single group, the thallo- 

 phytes, in which he establishes two series exactly parallel 

 — one comprising the forms with chlorophyle, the other, 

 the forms which are deprived of it." 



" The Bacteria, then, resemble green plants, in that 

 they assimilate nitrogen contained in their cells by taking 

 it from ammonia compounds, which animals cannot do, 

 They differ irom green plants in that they cannot draw 

 their carbon from carbonic acid, and only assimilate or- 

 ganic substances containing carbon, above all the hy- 

 drates of carbon and their derivatives; and in this re- 

 spect they resemble animals." 



Ehrenberg was the first to maintain that the motion of 

 Bacteria depended npon the presence of vibratile cilia 

 (observed by him in spirillum volutans), but although 

 the cilia, denied at first by most microscopists, have been 

 since seen in nearly all the bacteria, recent researches 

 permit us to say that cilia exist without doubt in all true 

 bacteria ; the botanist who has best studied them, M. 

 Walming for example, recognize that it is scarcely pro- 

 bable that these organs are the cause of their movement, 

 for one meets some examples in which the body remains 

 motionless, while the cilia are in violent agitation, and 

 others in which the body moves, while the cilia remain 

 inert or dragging behind. 



Cohn explains the origin of the gelatinous substance 

 in which the bacteria are included as being produced by 

 a thickening or jellification of the cell membrane, but a 

 more plausible view is that it is produced by a secretion 

 from their protoplasm. 



Mr. A. Agassiz has printed in the Proceedings of the 

 American Academy a biographical sketch of the late 

 Count Pourtales, together with a biographical list of his 

 principal publications. Mr. Agassiz has also written a 

 Review of Professor Haeckel's Monograph of the 

 Acalephs in the August number of the American Jour- 

 nal of Science. 



