"The figure below is a representation of one of the American photographs reduced about one-half. _V_ is the image of Venus, which, on the actual plate, is about a seventh of an inch in diameter; _aa'_ is the image of the plumb-line. The centre of the reticle is marked with a cross." [Illustration: Fig. 160.] The English photographs proved to be of little value, and the results of the measurements and calculations upon the American pictures have not yet been published. There is a growing apprehension that no photographic method can be relied upon. The most recent determinations by various methods indicate that the sun's distance is such that his parallax is about eighty-eight seconds. This would make the linear value of a second at the surface of the sun about four hundred and fifty miles. [Illustration: Plate 1.] II. PHYSICAL AND CHEMICAL CONDITION OF THE SUN. Physical Condition of the Sun. 143. _The Sun Composed mainly of Gas._--It is now generally believed that the sun is mainly a ball of gas, or vapor, powerfully condensed at the centre by the weight of the superincumbent mass, but kept from liquefying by its exceedingly high temperature. The gaseous interior of the sun is surrounded by a layer of luminous clouds, which constitutes its visible surface, and which is called its _photosphere_. Here and there in the photosphere are seen dark _spots_, which often attain an immense magnitude. These clouds float in the _solar atmosphere_, which extends some distance beyond them. The luminous surface of the sun is surrounded by a _rose-colored_ stratum of gaseous matter, called the _chromosphere_. Here and there great masses of this chromospheric matter rise high above the general level. These masses are called _prominences_. Outside of the chromosphere is the _corona_, an irregular halo of faint, pearly light, mainly composed of filaments and streamers, which radiate from the sun to enormous distances, often more than a million of miles. In Fig. 161 is shown a section of the sun, according to Professor Young. The accompanying lithographic plate gives a general view of the photosphere with its spots, and of the chromosphere and its prominences. 144. _The Temperature of the Sun._--Those who have investigated the subject of the temperature of the sun have come to very different conclusions; some placing it as high as four million degrees Fahrenheit, and others as low as ten thousand degrees. Professor Young thinks that Rosetti's estimate of eighteen thousand degrees as the _effective temperature_ of the sun's surface is probably not far from correct. By this is meant the temperature that a uniform surface of lampblack of the size of the sun must have in order to radiate as much heat as the sun does. The most intense artificial heat does not exceed four thousand degrees Fahrenheit. [Illustration: Fig. 161.]