ACADEMY OF NATURAL SCIENCES. 365 



easily read to tenths of a degree. All the barometers had been adjusted to or 

 compared with the standard, and all agreed with it except the one at Astoria, 

 which required a plus correction of three thousandths of an inch. 



The stations used were Astoria, Fort Vancouver, Fort Dalles, camp on slope 

 of Mt. Hood, and summit of Mt. Hood. Observations had been taken for 

 several years at Astoria for me by Louis Wilson, U. S. Tidal Observer, at 7. 

 a.m., 2, p.m., and 9, p.m., of every day, besides hourly observations for ten days 

 or more of each month. The cistern of this barometer is fifty-three feet above 

 mean low tide. 



At Fort Vancouver observations of the same character were commenced 

 July 1st of this year, and are still going on. At Fort Dalles similar observa- 

 tions have been made since July 10th. 



The observations at the camp on the mountain slope were commenced at 7, 

 p.m., on August 22d, and continued hourly (with few omissions) until 8, a.m., on 

 the twenty-fourth. The barometer at the summit was hung up at 1:30, p.m., 

 and allowed to stand a half hour in free air, but protected from the direct rays 

 of the sun. It was then adjusted and observed at 2, p.m., 2:15, p.m., and 2:30. 

 p.m., by Mr. Heuer and Mr. Best, independently, and the two records as shown 

 to me were essentially the same. The mean reading of the barometer reduced 

 to 32° Fahrenheit, was 19,941 inches, with an observed air temperature of 

 41°.7, and wet bulb of 31°.3. The height of Fort Vancouver above Astoria 

 was computed from the mean of the simultaneous observations taken during the 

 months of July and August. The height of the Dalles above Fort Vancouver 

 was deduced from the corresponding observations during twenty-one days in 

 July, together with those for the month of August. The height of the camp 

 on the mountain slope above Fort Vancouver, and also the height of that camp 

 above Fort Dalles, were then separately computed from the daily means of the 

 observations taken at the three stations during August 23d. The difference 

 between the two should give the same result as by the direct calculations between 

 Fort Vancouver and Fort Dalles ; but on account of the short period observed 

 on the mountain camp, a plus correction of a little over eight feet was found 

 necessary to the estimated height of that camp to make the three results agree. 



It then remained only to calculate the height of the summit of Mount Hood 

 above the mountain camp. The mean of the three observations of the barom- 

 eter was assumed as the nearest approximation we can have to the mean ] r as- 

 sure for that day, as the horary oscillation at the summit is unknown. With 

 regard to the mean temperature for that day, we have no positive data to deter- 

 mine it. We cannot take the observed temperature, as the observations were 

 taken during the hottest part of the day. 



By consulting the hourly observations of the thermometer at the camp, I find 

 the range there is between 63° and 43^.7, or nearly 20° ; and supposing nearly 

 as great a range of temperature on the summit, I have assumed the mean tem- 

 perature then for that day to be 34°. 



The following is the final result of the computations : 



