POPULAR MISCELLANY. 



861 



likely to bo ague. The ancient inhabitants 

 of the Campagna cleared it of disease by 

 draining it so dry that the bacteria could 

 not thrive in it. This is considered imprac- 

 ticable at present, and our Koman investi- 

 gators have turned their attention to the 

 best prophylactics against malarial poison. 

 The universal quinine is good, but there are 

 objections to its constant use, and arsenic, 

 cautiously administered, is suggested as 

 preferable. Professor Tommasi - Crudelli 

 recommends, as an alternative prophylactic, 

 decoction of lemon. The plantation of the 

 eucalyptus appears to have failed. Near 

 Rome, at the " Tre Fontane," where euca- 

 lyptus-trees have been grown with a special 

 view to settling the question of their virtue, 

 both the monks who inhabit the monastery 

 and the workmen whom they employ have 

 suffered as much as others. In one sum- 

 mer, when the Campagna was comparatively 

 free from malaria, the inhabitants and ser- 

 vants of the " Tre Fontane " suffered more 

 than the rest. Year before last. Professor 

 Tommasi-Crudelli advised the Italian Gov- 

 ernment to drain and cover with turf the 

 grounds of the Palazzo Salviati on the Lun- 

 gara, where the new military college has 

 been built. This was done. The result 

 was that no cases of malarial fever oc- 

 curred, while on the other side of the road 

 there were several that ended fatally. 



Inertia of the Eye and the Brain. — In a 



paper on the " Inertia of the Eye and the 

 Brain," Mr. James McKeen Cattell, of the 

 University of Leipsic, discusses, in view of 

 the results of experiments which he has 

 made, that part of the process of sensation 

 which concerns the time a light must work 

 on the retina in order that a sensation may 

 be excited. The time is to a considerable 

 extent dependent on the nature of the ob- 

 ject and the intensity of the light. It va- 

 ries with the several colors. Orange gives 

 the quickest impression, and yellow is hardly 

 behind it ; next come blue, red, and green ; 

 while the retina is least sensitive to violet 

 light, the time for which is from two to 

 three times as long as for orange. When 

 lamp-light is substituted for daylight, the 

 time required for perceiving the colors be- 

 comes longer, and the order is changed to 

 orange, red, yellow, violet, and blue. When 



the intensity of colored light varies, the 

 time increases in arithmetical progression as 

 the intensity decreases in geometrical pro- 

 gression. Applied to the distinction of 

 words and letters, the experiments showed 

 that Roman letters are more quickly per- 

 ceived than German letters, and that the 

 time is slightly shorter for words than for 

 letters, but longer for long or rare words, 

 and for words in a foreign language. The 

 simplest geometrical forms of the letters 

 seem the easiest to see ; all ornaments on the 

 letters hinder ; and it is doubtful whether it 

 is advantageous to use the thin lines or two 

 varieties of letters in printing. Our punctua- 

 tion-marks are hard to see, and Mr. Cattell, 

 believing them to be useless, suggests that 

 they might be replaced by spaces between 

 the words proportionate to the importance 

 of the pause. Some of the letters, as S and 

 C, are hard to recognize in themselves ; oth- 

 ers, as 0, Q, G, and C, are liable to confu- 

 sion by their similarity of form ; while E is 

 " needlessly illegible." The order of dis- 

 tinctness for the small letters is d, k, m, g, 

 h, b, p, w, u, 1, j, t, v, z, r, o, f, n, a, x, y, e, 

 i, g, c, 8. The letters are slightly more 

 difBcult to grasp than the numbers, for 

 every combination of numbers makes a 

 number that gives " sense." Not as many 

 words as letters can be grasped at one time, 

 but three times as many letters, when they 

 make words, and twice as many words when 

 they make a sentence, as when they have 

 no connection. The sentence is taken up 

 as a whole ; if it is not grasped, hardly any 

 of the words are read ; if it is grasped, the 

 words appear very distinct ; and this is also 

 the case when the observer constructs an 

 imaginary sentence from the traces he has 

 taken up. The personal equations were 

 important factors in all the experiments, 

 but they did not materially affect the re- 

 sults as wholes. 



The Problem of London Sewage.— Tlie 

 disposition of the sewage of London has 

 been made the subject of the report of a 

 royal commission, but still remains nearly 

 as dark as ever. The one point on which 

 all are agreed is that the present method of 

 turning the sewage and rainfall of the streets 

 into the river near the city is reprehensible 

 from every point of view, but it is almost 



