95. Method of Calculating Heights from Observations with the Mountain Thermometer; Example. 96. THERMOMETERS FOR ENGINEERS. CHAPTER XI. INSTRUMENTS FOR ASCERTAINING THE HUMIDITY OF THE AIR. 97. Hygrometric Substances. 98. SAUSSURE'S HYGROMETER. 99. Dew-Point. 100. DROSOMETER. 101. Humidity. 102. LESLIE'S HYGROMETER. 103. DANIEL'S HYGROMETER. 104. REGNAULT'S CONDENSER HYGROMETER. 105. Temperature of Evaporation. 106. MASON'S HYGROMETER. 107. SELF-REGISTERING HYGROMETER. 108. Causes of Dew. 109. Plan of Exposing Thermometers. CHAPTER XII. INSTRUMENTS USED FOR MEASURING THE RAINFALL. 110. HOWARD'S RAIN-GAUGE. 111. GLAISHER'S RAIN-GAUGE. 112. RAIN-GAUGE WITH FLOAT. 113. RAIN-GAUGE WITH SIDE TUBE. 114. FITZROY'S RAIN-GAUGE. 115. SELF-REGISTERING RAIN-GAUGE. 116. The principle of Measurement. 117. Position for Rain-gauge, &c. 118. Cause of Rain. 119. Laws of Rainfall. 120. Utility of Statistics of Rainfall. 121. NEW FORM OF RAIN-GAUGE. CHAPTER XIII. APPARATUS EMPLOYED FOR REGISTERING THE DIRECTION, PRESSURE, AND VELOCITY OF THE WIND. 122. THE VANE. 123. LIND'S WIND-GAUGE. 124. HARRIS'S WIND-GAUGE. 125. ROBINSON'S ANEMOMETER. 126. WHEWELL'S ANEMOMETER. 127. OSLER'S ANEMOMETER AND PLUVIOMETER. 128. BECKLEY'S ANEMOMETER. 129. SELF-REGISTERING WIND-GAUGE. 130. Anemometric Observations. CHAPTER XIV. INSTRUMENTS FOR INVESTIGATING ATMOSPHERIC ELECTRICITY. 131. ATMOSPHERIC ELECTROSCOPE. 132. VOLTA'S ELECTROMETER. 133. PELTIER'S ELECTROMETER. 134. BOHNENBERGER'S ELECTROSCOPE. 135. THOMSON'S ELECTROMETER. 136. Fundamental Facts. 137. Lightning Conductors. 138. Precautions against Lightning. CHAPTER XV. OZONE AND ITS INDICATORS. 139. Nature of Ozone. 140. SCHONBEIN'S OZONOMETER. 141. MOFFAT'S OZONOMETER. 142. CLARK'S OZONE CAGE. 143. Distribution and Effects of Ozone. 144. LANCASTER'S REGISTERING OZONOMETER. CHAPTER XVI. MISCELLANEOUS INSTRUMENTS. 145. CHEMICAL WEATHER GLASS. 146. LESLIE'S DIFFERENTIAL THERMOMETER. 147. ROMFORD'S DIFFERENTIAL THERMOMETER. 148. GLAISHER'S THERMOMETER STAND. 149. THERMOMETER SCREEN, FOR USE AT SEA. 150. ANEMOSCOPE. 151. EVAPORATING DISH, OR GAUGE. 152. ADMIDOMETER. 153. CLOUD REFLECTOR. 154. SUNSHINE RECORDER. 155. SET OF PORTABLE INSTRUMENTS. 156. IMPLEMENTS. 157. HYDROMETER. 158. NEWMAN'S SELF-REGISTERING TIDE-GAUGE. TABLES. PAGE Table of Corrections, for Capillary Depression of the Mercury in Boiled and in Unboiled Barometer-Tubes 6 Tables for Deducing Heights by means of the Barometer:-- No. 1. Approximate Height due to Barometric Pressure 42 No. 2. Correction for Mean Temperature of Air 44