Notes and Memoranda. 243 



to the extreme and violent changes which it undergoes in its rotation round the 

 sun. Halley's comet, for example, at one time approaches the sun to within 

 56 millions of miles, and then recedes to the enormous distance of 3370 millions 

 of miles. At the time of its perihelion, or least distance, it passes through one 

 heliocentric degree of its orbit in 157 hours, and receives in a given time 3600 

 times as much heat as when it reaches its aphelion, or greatest distance, in which 

 position its motion is so slow that 6J years are required for its passage through 

 one heliocentric degree. Thus it will be seen that comets with eccentric orbits 

 are subject to violent changes of temperature and velocity, which do not affect 

 planets whose orbits approximate more closely to the circular form, and from this 

 circumstance a greater electrical disturbance and excitation may possibly be pro- 

 duced. Mr. Marsh gives a table of remarkable comets, showing that those which 

 have exhibited the greatest splendour have been distinguished by extreme eccen- 

 tricity, while comets of small eccentricity have been inconspicuous. From this 

 law it follows that brilliant comets have long periods ; and he tells us that, with 

 the exception of Halley's comet, which performs its journey in seventy-six 

 years, no other first-class comet has a shorter period than one measured by 

 centuries. Mr. Marsh likens the tails of comets to auroral streamers, and con- 

 siders that their envelopes resemble the electrical discharges in Mr. Gassiot's 

 vacuum tubes, the luminous character being derived from the solid particles 

 which the electrical current transports from the nucleus, just as similar particles 

 are carried off from the electrodes in a voltaic discharge. 



Heiiography. — M. Chevreul, in presenting to the French Academy some 

 fresh researches of M. Niepce de St. Victor, explained two remarkable facts : " the 

 first is, that the image produced by the sun is direct, and not inverted, like those 

 obtained by ordinary methods ; the second is, that the light whitens the parts 

 which it strikes, through a special action of the dextrine and chloride of lead 

 varnish, while without this varnish it would impress a violet tint on the chloride 

 of silver of the daguerreotype plate — a remarkable result, since M. Niepce has 

 observed that the shadows of an engi-aving are reproduced in black on plates 

 prepared with his varnish. The colours of the image are not produced simul- 

 taneously ; for example, the yellow appears before the green, and when this latter 

 is manifested the yellow is weakened, if not effaced. Does it not follow from this, 

 < hat the way to reproduce the colours with fidelity would be by the use of 

 screens, so arranged as to cover the parts where the colours are first exhibited, so 

 as to give more time to other colours which require it?" 



M. FiiOURENS on Kespiration. — In a warm-blooded vertebrate animal, respi- 

 ratory movements are instantly arrested if the medulla oblongata is divided " in 

 the centre of the V of the gray matter," and the creature dies immediately. In 

 a frog, pulmonary respiration ceases on making a similar division,* but the animal 

 continues to live through its cutaneous respiration. The respiration of a fish 

 ceases if the medulla oblongata is divided by a section which passes just behind 

 the cerebellum, and the animal dies more or less quickly, according to the species. 

 M. Flourens observes — " The lobes, or cerebral hemispheres, minister to intelli- 

 gence, and that only ; the cerebellum is devoted to the co-ordination of the 

 movements of locomotion, and there is a point in the medulla oblongata which 

 presides over the movements of respiration." 



Connection between Human and Cattle Disorders. — Professor Gamgee, 

 in an article on the " Health of Stock," in the Edinburgh Veterinary Review, 

 states that he has noticed a remarkable connection between diseases in man and 

 in the lower animals ; he believes many of the former may be traced to unwhole- 

 some food. The same authority affirms that on the average 33£ per cent, of the 

 cows kept in any large town die annually of disease ; and he asks, " If our 

 sanitary reformers are alarmed at a mortality of two hundred persons in ten 

 thousand, what will they say to more than sixteen times that mortality amongst 

 our poor cows ?" 



* The "nceud vital" of the frog exists in "l'espece de pont que forme sur le 

 plancher du quatrieme ventricule, le cervelet, d'ailleurs tres-petit, de cea 

 animaux." — Comptes Bendus, p. 315, No. 6, 1862. 



