The Instant the Sound was heard; a gentle Motion was _impressed_ on the _Balloon_, as if by a Hand touching _it_ near the _Top_. 163. Clouds to the North-East appeared, for the first Time, in _rapid_ Motion towards the Balloon. They _sailed_ directly _under_ it: filled up the Chasm, and drew a _white_ Veil over _all terrestrial_ Objects. [Sidenote: Conjecture in the Cause of the Motion.] 164. It has been _since_ imagined, that a fresh Wind _descended_ from the South-West Quarter in the upper Current, and was heard in the North-East, being ecchoed from the upper Tier of Clouds _below_: and that the Balloon, finding less Resistance than the +range+ of Clouds, soon overtook and passed them: particularly as the lower Part of the _white_ Flag vibrated only in the usual Direction. 165. The _encreased_ progressive Motion of the Balloon was _not_ perceived (Section 18): being considered as at _Rest_, and the _apparent_ Motion _referred_ to the _Clouds_. CHAPTER XXIX. [Sidenote: A narrow Ditch the Duke of Bridgewater’s Canal.] Section 166. In a few Minutes, a Side-Break throu’ the Clouds discovered a long ill-formed narrow Line or Ditch, something less than a Foot in Breadth, extending several Ways: and which from its Proximity to Places that were known, and coming into View; viz. the Country about Norton and Halton-Castle; proved to be the Duke of Bridgewater’s Canal. [Sidenote: A Glympse of Runcorn Gap.] +Suddenly+ came in Sight the _spacious_ +open+ of the Mersey above Runcorn Gap: which appeared of a +ruddy+ Colour, and _very_ near: as if the Balloon had again _felt_ the Influence of the _River_. [Sidenote: _Balloon-Geography_ first suggested for _Maps_.] 167. A new System, that of _Balloon-Geography_ here suggested itself: in which the Essentials of _Proportion_ and _Bearings_ woud be far more accurate, than by the present Method, both for _Maps_ and _Charts_, viz. To make Drawings by +sight+, from the Car of a Balloon with a _Camera Obscura_, aided by a Micrometer applied to the under Side of _the transparent_ Glass. [Sidenote: Air presumed to be warm with South-West Wind long continued.] The Season proper for such an aironautic Expedition, would be _any_ _calm bright_ Day: the Wind having blown from the South West Quarter, for some Days before, which is _frequently_ the Case: the Air, at _such_ Conjuncture probably remaining +warm+, to the Height of a Mile or more, unless in the very Midst of Winter. [Sidenote: Balloon Geography for _Charts_.] 168. And particularly for Charts, which in a _maritime_ Country are _most_ useful: as Balloons have an extraordinary Predilection to become _stationary_ over Channels and Rivers; altho’ a very _strong_ Gale of Wind, shoud continue the _whole_ Time to blow in an horizontal Course directly +under+ the Balloon. [Sidenote: Balloon in a Calm with a _strong_ Wind _below_.]