7. An extraordinary stillness and stagnation of the air, both by day and night. Sometimes in the low-lying districts not a breath could be observed. Even when at more elevated stations the wind was moving with a force of 1 lb 7 oz., the pressure was only ¼ lb in the heart of London. Wind is the ventilator of nature. Artificial ventilation, as far as it is successful, is an imitation of nature’s process. It is stated on undoubted authority (Maitland’s History of London) that for several weeks before the Great Plague broke out in London, there was an uninterrupted calm, so that there was not sufficient motion of the air to stir a vane. Baynard, a contemporary physician, confirms this fact. The like circumstance is mentioned by Diemerbroeck in giving an account of the plague at Nimeguen. At the period when the last plague visited Vienna, according to Sir Gilbert Blane, there had been no wind for three months. The terrific outbreak of the cholera at Kurrachee was preceded for some days by such a stagnation of the atmosphere that an oppression scarcely to be endured affected the whole population. It is obvious that calms must favour the accumulation and concentration of effluvia from every source from which they arise. 8. A general deficiency in the tension of common positive electricity. 9. A deficiency of one fourth of the rain-fall for the year. During 118 consecutive days there was scarcely any rain, and not a single drop for 18 days at the period of the highest mortality. 10. A total absence of ozone at all the stations near the river, while at stations of high elevation it was of general occurrence. These observations relate particularly to the epidemic of 1854, which was more carefully watched than the two former; but the results are similar for each. “The three epidemics,” says Mr Glashier, in summing up the results of his inquiry, “were attended with a particular state of atmosphere, characterized by a prevalent mist, thin in high places, dense in low. During the height of the epidemic, in all cases, the reading of the barometer was remarkably high, the atmosphere thick; and in 1849 and 1854 the temperature above its average. A total absence of rain, and a stillness of air amounting almost to calm, accompanied the progress of the disease on each occasion. In places near the river, the night temperatures were high, with small diurnal range, with a dense torpid mist and air charged with the many impurities arising from the exhalations of the Thames, and adjoining marshes; a deficiency of electricity, and, as shown in 1854, a total absence of ozone, most probably destroyed by the decomposition of the organic matter with which the air in these situations is so strongly charged.