Ai^g. lo, 1876] 



NATURE 



321 



dark-coloured clouds, which gradually assumed the form of an 

 inverted cone pointing to the ground, and terminating in a long 

 sinuous band. A whitish sinuous column soon appeared sud- 

 denly between it and the ground, and rapidly enlarged upwards, 

 the whole phenomenon soon assuming the appearance of two 

 cones united at their summits. The lower cone, at first 

 lightish-coloured and in a certain degree transparent, gradually 

 assumed a darker shade, which was propagated from the base 

 towards the summit. When passing over the right bank of the 

 Loire, a dense mass of sand, mud, and fine gravel, was observed 

 drawn towards it ; in crossing the river a jet d'eau broken into 

 spray appeared in the form of a cone ascending the waterspout, 

 with its base resting on the water, the spray on all sides being 

 drawn inwards to^^■ards the axis in spires. It is said that an 

 undefined glimmering appearance preceded the column of as- 

 cending spray. On reaching the extensive sandy shore of the 

 left bank, clouds of sand were drawn violently in upon it, just 

 as happened with the spray of the river. From the value of 

 several of these points in tMe theory of waterspouts and other 

 aerial movements, it is desirable, as opportunity offers that they 

 be tested by observations made with the greatest accuracy and 

 skill. 



Mr. F. E. Nipher writes to the American Journal of 

 Science and Arts, that not long since, while writing lo.^a- 

 rithms that were being read to him, he observed that the 

 probability of error in writing the numbers appeared to be 

 much less at the extremities of the number than in the middle. 

 This he investigated at length in numbers of from five to 

 tea digits. It was found that the probability of error is in 

 all cases expressed by the terms of the expanded binomial 

 {a + (J)", where ti is a function of the number of digits, a and b 

 were, so far, always unequal with all the persons that had been 

 experimented on. The probability of error is greatest just after 

 the middle of the number. This led to an interesting investiga- 

 tion on the power of memory. Allowing definite intervals {t) of 

 time to elapse between the giving and the writing of the number, 

 it is evident that the number of errors will increase with the 

 value of t. In order to aid the experimenter in abstaining from 

 mentally repeating the number which he is to write, he is allowed 

 to determine the value of / by counting the beats of a seconds 

 pendulum. The investigation is yet in progress, but enough has 

 been done to develop the fact that the relation between the 

 number of figures (per 100) written correctly, and the values t, is 

 a logarithmic one. It is the same as the function expressing the 

 decrease in the amplitude of the beats of a pendulum in time, as 

 due to a resisting medium. 



We learn from the same journal that the trustees of the 

 Massachusetts Society for promoting Agriculture have offered 

 some very handsome prizes for special plantations within 

 the State of Massachusetts. In the first place, for the best 

 plantation of not less than five acres of larch, or on the Cape, 

 &c., of Scotch or Corsican pine, originally of not less than 

 2,700 trees to the acre, on poor, worn-out, or otherwise agri- 

 culturally worthless land, a prize of §1,000. For the next 

 best, a prize of $600; for the third best, §400, Next, for 

 the best plantation of the same extent with American white 

 ash, not less than 5,000 trees to the acre, a prize of 

 §600 ; for the next best, $400. Intending competitors must 

 notify the Secretary of the Society, E. W. Perkins, Jamaica 

 Plain, Boston, as early as December i, 1876, and plant in tlie 

 spring of 1877. Special directions, not only for planting and 

 caring for, but also for procuring trees for the purpose, are given 

 in a recently-published pamphlet by Prof. Sargent, of Harvard, 

 " A Few Suggestions on Tree-planting," which the Society has 

 reprinted for gratuitous distribution j and a citizen of Boston 

 patriotically offers to look after the importation of the seedling 

 trees, which, in such quantities, and for next year's planting, 



would have to be obtained mainly in Europe, at least the pincj 

 and larches. The ashes, probably, would have to be raised 

 from seed ; and the time, if need be, would doubtless be ex- 

 tended. The prizes are to be awarded in the summer of 1877. 



Among various experiments with the radiometer which have 

 lately been described to the French Academy, is one in which 

 M. Govi inclosed a very sensitive instrument (the vanes of which 

 were of polished aluminium on the one side and blackened mica 

 on the other) in a glass cylinder, into which was continuously 

 passed steam from boiling water. The radiometer began 

 quickly to rotate (the aluminium face first) immediately 

 the steam commenced to raise the temperature of the inclosure. 

 Ere long, however, the temperature becoming invariable, the 

 rotation diminished, and after a few minutes ceased altogether. 

 On stopping the entrance of steam, the instrument rotated anew, 

 but in the opposite direction, and did so for a long time before 

 stopping. Every motionless radiometer, IM. Govi points out, is 

 like the instrument stopped at 100° iii the above experiment. 

 To make it turn in the inverse direction, you have merely to put 

 it in a vessel of cold water ; the black faces then move first, and 

 the instrument only stops after a new state of thermal equilibrium 

 has been established On being brought out of the cold water it 

 turns as though it were struck by light, although it may be in 

 complete darkness. A radiometer motionless in the inclosure at 

 100°, or at zero, will turn anew if the light of a bright flame be 

 directed on the blackened face of its vanes ; ' ' because in both 

 cases the light absorbed by the blackened face then becomes 

 heat, which is added to that which the vanes possess already, 

 and may consequently further liberate gas from them." In an 

 experiment described by M. Ducretet, ether is poured on the enve- 

 lope of a radiometer which moves with direct rotation (black surf- 

 aces repelled) in moderate daylight. The motion is arrested and 

 changed to that in the inverse direction. This reaction pre- 

 sently ceases, and the vanes resume the original direct motion, 

 notwithstanding the evaporation maintained on the envelope by 

 a light sprinkling of ether. The rotation now becomes more 

 rapid than it was at first, the evaporation apparently acting as 

 a source of heat, and yet the lowering of temperature through 

 evaporation is very perceptible. When the sprinkling with ether 

 ceases, the motion resumes its normal velocity and ttmaxas direct. 

 M. Ducretet also tried the effect of phosphorescent powders on 

 the radiometer, but got no motion. 



The number of visitors to the Loan Collection of Scientific 

 Apparatus during the week ending August 5 was as follows : — 

 Monday, 2,951 ; Tuesday, 3,377; Wednesday, 488; Thursday, 

 441 ; Friday, 441 ; Saturday, 3,422 ; total, 11,120. 



An interesting contribution to the study of the eye affection 

 known as neuro-paralytic keratitis, by Dr. Decker, has just 

 appeared in the Archives des Sciences. He arrives at the follow- 

 ing conclusions :—(i) It is not an ordinary traumatic keratitis. 

 (2) It results from the combined action of two orders of things, a. 

 determining causes, which are the exterior modifying agents ; 

 b. a predisposing cause, consisting in diminution of the resistance 

 of the eye, the most exposed parts of which (cornea), become 

 easily altered by the determining causes. (3) This vulnerability 

 is the result of lesion of nerve fibres in the internal side of the 

 trigeminus. 4. These are neither sensitive nor vasomotor 

 nerves. 5. The hypothesis that they are trophic nerves best 

 accounts for the facts observed. 6. Anatomically, neuroparalytic 

 keratitis consists of a primary necrosis of the central part of the 

 cornea (if the latter be left open), followed in a short time by a 

 secondary inflammation of the peripheric parts, and of the con- 

 junctiva. 



MM. Becquerel give a brief notice in the Bulletin Heb- 

 domadaire. No. 456, of the Scientific Association of France, 

 of the observations of temperature made at the Museum of 



