152 ANNUAL KECOKD OF SCIENCE AND INDUSTRY. 



that for temperatures above freezing, the psychrometer gives, 



with Kegnault's tables, the same quantity of moisture as is 

 found by chemical methods of observation. His fixed ane- 

 mometer was investigated by means of a similar portable 

 standard, and found to require corrections amounting to ten 

 per cent, of the whole wind velocity. By placing anemome- 

 ters upon different portions of a railroad train, he investigat- 

 ed the variations in the flow of air past the train, but could 

 only be thereby led to a very general confirmation of the re- 

 sults given by other methods as to the accuracy of the ane- 

 mometer. 



Among the scientific papers published in the memoirs and 

 notices of the current volume of the Meteor ologia Itallana, 

 we have received a timely paper, by Dr. Chistoni, on a Com- 

 parison of the Kegnault Dew-point Apparatus, August's Psy- 

 chrometer, and the Ventilation or Whirling Hygrometer, 

 which was first recommended by Belli a subject that is now 

 very generally attracting attention ; and it is probable that 

 the demand for increasing accuracy in meteorological data 

 will soon require that the psychrometer be left to second- 

 class observing -stations, and that the standard observers 

 adopt either dew-point instruments or chemical methods. 



Chistoni concludes that, under a barometric pressure of 

 about 30 inches, and at temperatures of about 50 Fahr., the 

 psychrometre a fronde will give the tension of vapor to 

 within a tenth of a millimeter, and the relative humidity 

 precise to within five per cent. 



A modification of Kegnault's dew-point apparatus has been 

 invented by Alluard, Director of the Observatory at Cler- 

 mont. It is essentially a square brass tube, gilt and highly 

 polished, containing the ether to be evaporated, and also a 

 thermometer to indicate its temperature; the air-tempera- 

 ture being shown by an exterior thermometer. The dew is 

 deposited upon a flat surface, and can be seen at a great dis- 

 tance, by contrast with a contiguous polished surface. 



A cheap and serviceable self-recording anemometer, giving 

 velocity and direction, is described by Nipher in the last vol- 

 ume of the Transactions of the St. Louis Academy. He also 

 contributes a note on the discordances as to velocity as regis- 

 tered by anemometers only a short distance apart, which al- 

 though he does not so state are evidently due in large part 



