Two Essays: One Upon Single Vision with Two Eyes; the Other on DewA Constable and Company, 1818 - 439 pages Contains possibly the first statement of the theory of natural selection; as well as the theory of dew and a classic work in meteorology and in environmental and industrial medicine and vision. |
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Common terms and phrases
afterwards Aguilonius Alhazen apparent directions appear single Aristotle atmosphere attract dew bodies calm nights cause centres circumstances clear and calm clouds colour common axis conse consequently considerable contrary cornea dewy nights distance distinctly earth equally Essay experiments exposed fact feet formation of dew former glasses grains of wool grass grassplat gravel walk greater ground heat hoarfrost hole horopter inches inclination intersection latter left eye less luminous point ment mentioned metal middle moisture motion muscles observed occasioned occurred opinion optic axes orange colour Patrick Wilson perceived person plane Porterfield posi position production of dew pupils quantity of dew radiation raised board rays reason refractive refractive power Reid respect retina right eye seen single serene nights side sight similar situated sky at night snow spect spot substances supposed swandown temperature theory thermometer tion visible direction visual base warmer watery vapour weather weight
Popular passages
Page 194 - Dense clouds, near the earth, must possess the same heat as the lower atmosphere, and will therefore send to the earth, as much, or nearly as much heat as they receive from it by radiation. But similarly dense clouds, if very high, though they equally intercept the communication of the earth with the sky, yet being, from their elevated situation, colder than the earth, will radiate to it less heat than they receive from it, and may, consequently, admit of bodies on its surface becoming seyeral degrees...
Page 241 - ... the air several feet above the ground and the unsheltered grass, did not exceed 5°, the sheltered grass was about as warm as the air. If that difference, however, exceeded 5°, the air was found to be somewhat warmer than the sheltered grass. Thus, upon one night, when fully exposed grass was 11° colder than the air, the latter was 3° warmer than the sheltered grass ; and the same difference existed on another night, when the air was 14° warmer than the exposed grass. One reason for this...
Page 408 - Africa, some one would be better fitted than the others to bear the diseases of the country. This race would consequently multiply, while the others would decrease ; not only from their inability to sustain the attacks of disease, but from their incapacity of contending with their more vigorous neighbours. The colour of this vigorous race I take for granted, from what has been already said, would be dark. But the same disposition to form varieties still existing, a darker and a darker race would...
Page 241 - ... small sticks, and there was no substance to radiate heat downwards to the latter grass, except the cambric handkerchief. The temperature of the grass, which was thus shielded from the sky, was upon many nights afterwards examined by me, and was always found higher than that of neighbouring grass which was uncovered, if this was colder than the air. When the difference in temperature, between the air several feet above the ground and the unsheltered grass, did not exceed 5°, the sheltered grass...
Page 379 - ... impolitic, but would also be a very wicked thing; if every such law were a snare for the conscience of the subject. But in these cases the alternative is offered to every man ; " either abstain from this, or submit to such a penalty:" and his conscience will be clear, whichever side of the alternative he thinks proper to embrace.
Page 170 - I had many years, as was formerly mentioned, held the same opinion ; but I began to see reason, not long after my regular course of experiments commenced, to doubt its truth, as I found that bodies would sometimes become colder than the air, without being dewed ; and that, when dew was formed, if different times •were compared, ' its quantity, and the degree of cold which appeared with it, were very far from being always in the same proportion to each other.
Page 406 - ... smallpox, differs in no observable thing from another, which is still liable to be affected with that disease. Regarding then as certain, that the negro race are better fitted to resist the attacks of the diseases of hot climates than the white, it is reasonable to infer, that those, who only approach the black race, will be likewise better fitted to do so, than others who are entirely white. This is, in fact, found to be true, with regard to the mixture of the two races; since mulattoes are...
Page 133 - ... notwithstanding that it presented a greater surface to the air than the other parcel. On another night, 10 grains of wool gained on the raised board 19 grains, but the same quantity suspended in the air, on a level with the board, only 13 ; and on a third, 10 grains of wool acquired, on the same board, 2...
Page 240 - I had often, in the pride of half knowledge, smiled at the means frequently employed by gardeners, to protect tender plants from cold, as it appeared to me impossible, that a thin mat, or any such flimsy substance, could prevent them from attaining the temperature of the atmosphere, by which alone I thought them liable to be injured. But, when I had learned, that bodies on the surface of the earth become, during a still and serene night, colder than the atmosphere, by radiating their heat to the...
Page 201 - Bodies, exposed in a clear night to the sky, must radiate as much heat to it during the prevalence of wind, as they would do if the air were altogether still. But in the former case, little or no cold will be observed upon them above that of the atmosphere, as the frequent application of warm air must quickly return a heat equal, or nearly so, to that which they had lost by radiation. A slight agitation of the air is sufficient to produce some effect of this kind ; though, as has already been said,...