Retrospect of Philosophical, Mechanical, Chemical, and Agricultural Discoveries, Volumen6J. Wyatt, 1811 |
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Página 280 - ... sand ; and in the salt prepared from Cheshire brine, it is almost entirely carbonate of lime. The insoluble part of the less pure pieces of rock salt is chiefly a marly earth, with some sulphate of lime. The quantity of this impurity, as it is stated in the table, is considerably below the...
Página 21 - In very acute angles with the current it appears, that the centre of resistance in the sail does not coincide with the centre of its surface, but is considerably in front of it. As the obliquity of the current decreases, these centres approach, and coincide when the current becomes perpendicular to the sail. Hence any heel of the machine backward or forward removes the centre of support behind or before the point of suspension...
Página 21 - The stability in this position, arising from the centre of gravity being below the point of suspension, is aided by a remarkable circumstance that experiment alone could point out. In very acute angles with the current it appears that the centre of resistance in a sail does not coincide with the centre of its surface, but is considerably in front of it. As the obliquity of the current decreases these centres approach and coincide when the current becomes perpendicular to the sail. Hence any heel...
Página 21 - ... resistance by its new position, and that which is required to sink has lost it; so that as much power operates to restore the equilibrium in this case as tended to destroy it in the other, the operation very much resembling what takes place in the common boat. This angular form, with apex downwards, is the chief basis of stability in aerial navigation...
Página 391 - ... 9. The barometer should be observed occasionally thrice in the day, or oftener when the weather is changeable, in order to notice whether the mercury be stationary, rising or sinking; for from this circumstance, together with the direction of the wind and the apparent state of the air at the time, is information to be collected, and a continuance of the same, or a sudden change of the weather, to be foreseen.
Página 23 - A fifth mode of avoiding leverage is by using the continued action of oblique horizontal flyers, or an alternate action of the same kind, with surfaces so constructed as to accommodate their position to such alternate motion, the hinge or joint being in these cases vertical. In the construction of large vessels for aerial navigation a considerable portion of fixed sail will probably be used, and no more surface will be allotted towards gaining the propelling power than what is barely necessary, with...
Página 391 - ... 3. The atmosphere becoming clear, and the barometer above changeable, and rising, indicate fair weather. 4. The atmosphere clear, and the barometer near fair, and rising, denote continued fair weather. 5. Our prognostic of the weather is to be guided relatively, thus : if, notwithstanding the sinking of the barometer, little or no rain follow, and it afterward rise, we may expect continued dry weather.
Página 391 - ... points, and the thermometer sinking towards 32. A fall of snow seldom comes without a previous frost of some duration, and is indicated by the sinking of the barometer, especially if the mercury be below changeable, and the thermometer at or near the freezing point. When the temperature of the air is about 35, snow and rain sometimes fall together ; at a warmer temperature than 35, it seldom snows, or rains at a colder temperature.
Página 7 - I know that thirteen days of eight hours each, are well employed in dividing such a circle by my method ; about fiftytwo days would be consumed in doing the same thing by BIRD'S method ; and I think I cannot err much when I state the method by adjustment, supposing every dot to be tried, and that two-thirds of them want adjusting, to require about one hundred and fifty of such days. The economy of time ( setting aside the decided means of accuracy ) which the above estimate of its application offers...
Página 4 - ... distant. Now, the microscopes remaining fixed, turn the circle half round, or until the first microscope coincides with the opposite dot; and, if the other microscope be exactly at the other dot, it is obvious that these dots are 180" apart, or in the true diameter of the circle ; and if they disagree, it is obvious that half the quantity by which they disagree, as measured by the divisions of the micrometer head, is the error of the opposite division ; for the quantity measured is that by which...