Page:Popular Science Monthly Volume 16.djvu/357

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THE MOST POWERFUL TELESCOPE.

duce any of them by any process analogous to that employed for vaccination.

All these reports and facts relate to vaccinations performed with humanized lymph, and previous to 1876. The most careful examination of every reported or suspected case among the 126,000 vaccinations performed up to that time failed to furnish a single case of the transmission of disease of any kind whatsoever from one person to another by means of vaccination.

In order, however, to avoid as far as possible the prejudice which was at one time so widespread in this matter, no humanized lymph has been used by the Vaccinating Corps for nearly three years. All the virus now used is eighth-day lymph taken from healthy calves carefully selected and kept in the country under the supervision of the inspector, exclusively for this purpose.

No very special advantage is claimed at present for this over properly selected humanized lymph; if, however, any difference is observable in the results, it is in favor of the bovine lymph, as affording fewer cases of troublesome inflammation.

One advantage is decided: it has tended to diminish a prejudice, and so remove in some degree an objection to vaccination.

It is in the face of an abundance of facts such as these, instead of the badly observed and badly studied facts of fifteen years ago, that intelligent people now must doubt the safety and utility of vaccination.

 
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THE MOST POWERFUL TELESCOPE IN EXISTENCE.
By E. NEISON, F. R. A. S.

WHICH is the most powerful telescope in existence? Define the meaning which ought to be attached to the adjective "powerful" in this question. The most powerful telescope in existence is that existing telescope which can do the most work. The work of a telescope may be said to be to enable you to see and to enable you to measure. Therefore, that telescope with which you can see most and can measure best is that which can do the most work, and is unquestionably the most powerful telescope in existence.

Which is the most powerful telescope in existence?

Every one has heard of the two giant telescopes which were constructed nearly forty years ago by the late Lord Rosse, and which were erected at his residence at Parsonstown, about fifty miles from Dublin. The first great telescope constructed by Lord Rosse was a reflecting telescope with a speculum three feet in diameter and twenty-six feet in focal length. It was carried in a ponderous tube moving in a massive iron mounting by means of ingenious machinery. When