The meaning of "and then the lover sighing like furnace" in William Shakespeare’s “The Seven Ages of Man” from his comedy As You Like It is that the passion and expression of love can be akin to the heat and breathing of a furnace. Shakespeare writes of a lover heaving a sigh like a furnace and this could be because of a yearning for his heart’s desire – his lover. Therefore, there is an indication here of pining for a loved one, as if the lover cannot wait to see her again to enjoy time with her.
Conversely, the sighing could be because of unrequited love as well. In relationships, a heartfelt sigh can be expressed when a love relationship is not going as intended. One of the individuals may desire a deeper relationship; the other individual may want to tone things down or end a relationship. Consequently, the sigh is more like a groaning – a groaning furnace – that signifies the lover is exasperated and may feel that love is lost. It could be that the heat is going out of the relationship.
The sighing is made to his “mistress’ eyebrow.” This indicates that he is trying to really get her attention – looking at her directly in her eye area. In addition, the indication here is that his lover is of fine beauty and her eyes and eyebrow features may be her most lovely characteristics. As a result, her lover concentrates on these features as he desires and aches for her. Nonetheless, the lover does sigh for her “with a woeful ballad.” This could mean that he is lonely and separated from her and longs to be with her. Time and circumstance may be preventing this.
Moreover, the lover may be sighing with this sad song because he may feel that their relationship is deteriorating. It could be that she fancies another and this lover knows that. William Shakespeare is showing the seven ages of man and how young love is a driving force in life. People often seek to find someone that they can spend the rest of their lives with, but it is not a simple exercise and the results are not always what one hopes for. Therefore, the result can be instances of lovers sighing like furnaces as the strong feelings of love play out in relationships.