440 



SCIENCE. 



[Vol. VII., No. 171 



hill, and whirling: the thermometer, to read it at 

 intervals until the bottom was reached. A return 

 trip was then begun, and the temperature obtained 

 again at the top of the hill. Later, minimum ther- 

 mometers were similarly exposed at both places, and 

 their readings compared. Early on clear mornings, 

 and at night, the temperature was usually found sev- 

 eral degrees lower in the valley, and differences of 

 ten degrees were not uncommon. At 7 a.m. on the 

 morning of Feb. 18, the temperature at the observa- 

 tory was Si° below zero. On descending the hill, the 

 thermometer fell rapidly, and at the bottom of the 

 valley read 18° below zero. The fall was greatest 

 along the steepest decline, and in one place fell three 

 degrees within twenty-five feet. Returning, the 

 thermometer rose rapidly, and at the top of the hill 

 again read below zero. 



During the continuance of these observations, 

 Professors Pettee and Schaeberle kindly consented 

 to take simultaneous observations of temperature 

 with those at the observatory. One lived about a 

 mile to the south-west, and the other about the same 

 distance to the west. Professor Pettee was at about 

 the same level as the observatory, and his readings 

 differed but little from the observatory readings ; 

 but the observations taken at the home of Professor 

 Schaeberle, which was at a considerably lower level, 

 several times gave temperatures ten degrees lower 

 than those at the observatory. These lower tem- 

 peratures, observed both in the adjacent valley and 

 at the home of Professor Schaeberle, were only 

 found at night and on clear, quiet mornings, and 

 disappeared in the middle of the day and in cloudy 

 weather. They were due, no doubt, to the fact that 

 the air most cooled by radiation, or by contact with 

 the earth's surface thus cooled, was heaviest, and 

 sunk to the lowest levels. In the middle of the day 

 the temperature was usually found slightly higher in 

 the valley than at the observatory. 



It seems evident, then, that for scientific purposes 

 which are intended for the study of temperature 

 changes over large sections of country, and where 

 stations can only be obtained many miles apart, it is 

 necessary to avoid these merely local differences of 

 temperature ; and the only method of eliminating 

 them is to get above them : in other words, wher- 

 ever irregularities in the earth's surface exist, the 

 thermometer should be on, or at least as high as, 

 that of any considerable portion of land surrounding 

 it, and not in valleys. The thermometer should, if 

 possible, be away from buildings, and as many feet 

 above ground as convenient. The best form of 

 shelter is probably that devised and described by 

 Professor Hazen. I have found bv comparison that 

 thermometers placed in accordance with these 

 considerations differ but little in their readings, 

 though they are many miles apart in a horizontal 

 direction. But scientific people should not fall into 

 the error of supposing that thermometers so placed 

 represent the temperature over the adjacent country. 

 The position is merely that in which local influences 

 are attempted to be avoided ; and it is not safe to 

 say to persons that their observations must be erro- 

 neous because they differ from those of the signal ser- 

 vice or some observatory. 



This is a subject 1 think well worthy of the con- 

 sideration of those in charge of state wpather ser- 

 vices. H. Helm Clayton. 



Blue Hill observatory. 

 Readville, Mass., April 16. 



Double vision. 



Since my earliest boyhood, or for more than fifty 

 years, I have had double vision and stereoscopic 

 eyes, which I have probably exercised more than a 

 million times. I have exercised the double vision to- 

 such an extent that it has become to a certain degree 

 compulsory, as, if I look at an object forty feet more 

 or less distant, all intervening objects are doubled 

 involuntarily. 



I often stereoscope (if that be a good verb) wall- 

 papers and carpets, if figures be of proper size, ar- 

 rangement, and distance. This has a wonderful 

 effect, producing the following changes : the walls 

 of an ordinary room are apparently thrown to a dis- 

 tance of a hundred feet, and are proportionately in- 

 creased in size. Any defects in the putting-on of 

 the paper will exhibit themselves in the same man- 

 ner as I shall mention when describing the effects on 

 gratings or lattice-work. The borders of the paper, 

 if not ' stereoscoped ' at the same time, with all 

 pictures, etc., on the walls, will remain at their 

 proper distances, and seem suspended in the air, 

 like Mohammed's coffin. The surface of the paper 

 is also remarkably increased in brilliancy. In 

 ' stereoscoping ' common photographs, they are 

 thrown to a much greater distance, and the proper 

 stereoscopic effect is brought about in the middle one 

 of the three. I suppose this accounts for the in- 

 creased size of the walls of rooms when so treated. 



What has bothered me the most is the effect on 

 gratings and lattice-work. In a piece of lattice- 

 work, say, eight by ten feet, and the eyes five feet 

 distant, the work is broken up, and has, instead of 

 a common surface, an apparent depth of three or 

 four feet. In some places there will be but a single 

 piece ; in other places two or three will be together 

 with their parallelism properly preserved. I sup- 

 pose that it is brought about by irregularities in the 

 construction of the diagonals in the structure ; but I 

 do not know enough about optics to explain this 

 peculiar breaking-up, and differences in apparent 

 distances of the different pieces making up the work. 

 The same effects are produced in looking down at 

 gratings in pavements. Geo. Keller, M.D. 



Bucyrus, O., May 10. 



Partition of Patagonia. 



The geographical note on the ' Partition of Pata- 

 gonia ' in the current issue of Science (No. 170) calls 

 to mind your recent strictures on cartographers for 

 failing to keep our school maps up to the times. It 

 would be but fair to state that the cartographers are 

 not delinquent in this instance. The treaty of parti- 

 tion was concluded at Buenos Ayres, July 23, 1881, 

 — five years ago. For the last three years all our 

 more popular school geographies have shown the 

 boundaries of Chili and the Argentine Republic as 

 determined by this treaty. Russell Hinman. 



Cincinnati, May 10. 



An old-time salt-storm. 



Can any of your readers tell me the exact date of 

 the so-called ' salt-storm ' which came upon the coast 

 of Massachusetts about 1815 ? As described by 

 old inhabitants, there was a high wind and heavy 

 rain, and the houses and all objects within a mile of 

 the water were coated with salt. Are such storms 

 of frequent occurrence, and what is their explana- 

 tion ? H. C. 



Salem, Mass., May 10. 



