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THE POPULAR SCIENCE MONTHLY. 



is in an excitable or irritable state from ill 

 health or any other cause, and is enough to 

 explain all tbe phenomena under considera- 

 tion. The visions most often correspond to 

 our previous experiences, and therefore re- 

 present objects we know. Sometimes, how- 

 ever, the images are unfamiliar, and they 

 are then referred to objects that we have 

 seen, but have ceased to remember in our 

 natural condition. The apparitions are thus 

 explained as the creatures of our imagina- 

 tion, which, through some brain-disturbance, 

 is enabled to project its visions forward on 

 the seats of sense, just as the ringing in the 

 ears, with which we are all familiar, is pro- 

 duced by some irritation of the hearing- 

 center of the brain. 



Soils as Filters. Dr. Victor C. Vaughan, 

 of the University of Michigan, has described 

 in "The Sanitarian" some experiments 

 which he has made to determine the power 

 of soils to prevent the filtration of organic 

 matter in solution. They had reference to 

 the questions, To what extent are organic 

 substances removed from solution by filtra- 

 tion through the soil ; and do different soils 

 differ in their capability of thus removing 

 organic matter ? Urea was selected as the 

 substance with which the experiments should 

 be tried, and urine as the fluid with which 

 filtration should be performed. The ordi- 

 nary gravel soil of Michigan was found to 

 produce but little effect in detaining the 

 urea, while it soon became saturated ; and 

 the conclusion was drawn that the secre- 

 tions from a family of six persons each day 

 would be sufficient, when properly dissolved, 

 to saturate more than seven cubic feet of 

 this soil, and that only a few weeks or 

 months would suffice, with a proper amount 

 of rainfall, to saturate every cubic foot of 

 soil to the depth of five or ten feet in a 

 small yard. Gravel, however, is the poorest 

 of filters, for the spaces between the parti- 

 cles allow the liquid to run through freely 

 at certain points. Sand and loam exhibited 

 a more satisfactory action, the loam more 

 so than the sand, both these substances 

 receiving a perceptibly larger quantity of 

 urea before they were saturated. This is 

 probably owing partly to their greater uni- 

 formity of constitution, in consequence of 

 which water can not run as fast through 



them as through gravel, and partly to their 

 greater porosity, by means of which matter 

 passing through them is more closely ex- 

 posed to the action of oxygen, the most 

 efficient agent for the destruction of organic 

 impurities. 



Freezing of a Lake by Radiation. A 



remarkable instance of the freezing of wa- 

 ter in consequence of the radiation of heat 

 was remarked in the Lake of Morat, Switzer- 

 land, after the cold weather of March last. 

 The lake, of which three fifths of the sur- 

 face had been covered with ice, was clear 

 on the Sth of March, and the weather had 

 become warm. During the night of the 

 10th of March, the thermometer did not de- 

 scend to the freezing-point ; yet on the 

 morning of the 11th the lake was covered 

 over with a thin sheet of ice. The Lakes 

 of Neufchatel and Constance were similarly 

 covered. The freezing is accounted for by 

 supposing it to have been occasioned by 

 the rapid and great radiation of heat which 

 took place on a perfectly clear night. An in- 

 tense degree of cold had been necessary to 

 cause the lakes to freeze during the cloudy 

 weather of the previous cold spell, and the 

 freezing was then very irregular and un- 

 equal. 



Effects of Diseased Meat. Mr. Julius 

 Hardwicke, F. R. C. S., an English local 

 medical officer of health, recently read a 

 paper at a sanitary meeting on " Meat as 

 Food for Man," in which he considered the 

 effects of diseased meat on the human sys- 

 tem. The evidence on this subject is of 

 the most conflicting character. According 

 to Dr. Letheby, enormous numbers of ani- 

 mals that died of rinderpest in 1863, and 

 more recently of pleuro-pneumonia, have 

 been sent to the London market and eaten 

 without having produced any tangible ef- 

 fects ; the Scotch eat " braxy " mutton 

 with impunity, and, some say, even prefer 

 it to sound mutton; and the people of 

 Paris must have eaten much diseased meat 

 during the siege, though we have no account 

 of their having suffered from the effects of 

 it. The symptoms or complaints of those 

 supposed to be suffering from having eaten 

 diseased meat are very similar to those oc- 

 casioned by the use of putrid meat. Para- 



