CHAPTER IV. 



SECTION I. 



REMARKS ON THE BAROMETRICAL OBSERVATIONS. 



My barometer was a new syphon, by Bunten, not compared with any other baro- 

 meter. It has not been practicable to carry it everywhere during the explorations, 

 sometimes because of the extreme risk which such a fragile instrument undergoes 

 in a rough region of precipices, swamps, rivers, and thickets, and at others, from 

 the necessary delay it occasions when time is to be economized. 



For heights on the Penokie Range, by observations not near each other in regard 

 to time, I have adopted as a base the average of sixty-nine readings at the lake- 

 level during two months, the elevation of the Lake being assumed at six hundred 

 and twenty-four feet above the ocean, — its true level not being yet determined. 



The season was very wet and cloudy, and in the mountain region, rains, par- 

 ticularly thunder-storms, occurred when the weather in the lowlands and on the 

 Lake, a few miles distant, was calm and clear. I should have adopted two bases, 

 one for fair weather and one for foul, if my observations had not shown nearly as 

 great variations in the height of the mercury, during weather and winds apparently 

 the same, as between fair and foul. In a region like that opposite La Pointe, 

 where a high range of mountains, within fifteen and twenty miles, overlooks a flat 

 country, and the Lake, the barometer appears to be influenced by causes that can- 

 not be perceived and noted at the time of the observation. Storms, winds, and 

 clouds, not visible to the eye, may yet be within the range of action upon the mer- 

 curial column. Thus, on the 14th of July, at fifteen feet above lake-level, ten 

 miles from the Lake, on Bad River, at 12 \ p. m., the column stood at 75*82 milli- 

 metres; attached thermometer, 61'4° Fahrenheit; detached, 61° ; breeze, southeast; 

 clear. On the 20th of August, seven feet above lake-level, 11 £ a.m., barometer, 

 74 - 07; attached thermometer, 68 - 6°; detached, 70°; breeze, southeast; clouds 8. 

 This is the extreme range of my readings, and the circumstances, excepting clouds, 

 apparently the same. My elevations, many of them the result of a single one, or 

 of but a few observations at each point, and often in heavy weather, must be looked 

 upon as approximations only ; in fact, all calculations from a single barometer, without 



