The division of descriptive and scientific texts into sense-groups depends largely on the lexico-grammatical structure of the sentences constituting the text. In other words, the length of a sense-group is determined by the syntax. But in the majority of cases a sense-group contains from two to four stressed (notional) words.
The tonetic pattern of a sense-group is characterized by:
A wide use of falling tones / a High Narrow Fall in non-final sense-groups
Gradually Descending, Broken Descending and Sliding Scales;
A Descending contour (tune);
The Mid Pitch Range;
In this style the decentralized stress is most frequent. The main rhythmic units in this style are a rhythmic group and a sense-group. The rhythm is based on a regular recurrence of stressed syllables and similar tonetic patterns of sense-groups.
The tempo is moderate and mostly constant.
Logical pauses are prevailing in descriptive and scientific prose. The longest pauses occur at the end of syntactical wholes. Shorter pauses occur at the end of sentences and sense-groups.
E.g. It wasˋlate the following afterˏnoon | when 'Soames 'stood in the ↑dining-room ˋwindow | 'gazing 'gloomily into theˋSquare. The 'sunlight still 'showed on theˋplane-trees, | and in the 'breeze their ↑gay 'broad 'leaves shone and ˏswung | in 'rhyme to a ˋbarrel organ at the ˎcorner. It was 'playing aˋwaltz, | an 'old waltz that was 'out of ˎfashion, | with a 'fateful 'rhythm in theˎnotes; | and it ˏwent 'on and →on, | though 'nothing inˋdeed but ˋleaves danced to the ˎtune.